@article{KleinpeterHeydenreichShainyan2021, author = {Kleinpeter, Erich and Heydenreich, Matthias and Shainyan, Bagrat A.}, title = {At the experimental limit of the NMR conformational analysis}, series = {Organic letters}, volume = {23}, journal = {Organic letters}, number = {2}, publisher = {American Chemical Society}, address = {Washington}, issn = {1523-7060}, doi = {10.1021/acs.orglett.0c03878}, pages = {405 -- 409}, year = {2021}, abstract = {The low temperature (95 K) NMR study of 1-Ph-1-t-Bu-silacyclohexane (1) showed the conformational equilibrium to be extremely one-sided toward thePh(ax),t-Bueq conformer. The barrier to interconversion has been measured (4.2-4.6 kcal/mol) and the conformational equilibrium [Delta nu = 1990.64 ppm (Si-29), 618.9 ppm (C-13), 1-Ph-ax:1-Pheq = (95.6-96.6\%):(3.4-4.4\%), K = 25 +/- 3, Delta G degrees = -RT ln K = 0.58-0.63 kcal/mol] analyzed. The assignment and quantification of the NMR signals is supported by MP2 and DFT calculations.}, language = {en} } @article{BelasriTopalHeydenreichetal.2020, author = {Belasri, Khadija and Topal, Leila and Heydenreich, Matthias and Koch, Andreas and Kleinpeter, Erich and Fulop, Ferenc and Szatmari, Istvan}, title = {Synthesis and conformational analysis of naphthoxazine-fused phenanthrene derivatives}, series = {Molecules}, volume = {25}, journal = {Molecules}, number = {11}, publisher = {MDPI}, address = {Basel}, issn = {1420-3049}, doi = {10.3390/molecules25112524}, pages = {15}, year = {2020}, abstract = {The synthesis of new phenanthr[9,10-e][1,3]oxazines was achieved by the direct coupling of 9-phenanthrol with cyclic imines in the modified aza-Friedel-Crafts reaction followed by the ring closure of the resulting bifunctional aminophenanthrols with formaldehyde. Aminophenanthrol-type Mannich bases were synthesised and transformed to phenanthr[9,10-e][1,3]oxazines via [4 + 2] cycloaddition. Detailed NMR structural analyses of the new polyheterocycles as well as conformational studies including Density Functional Theory (DFT) modelling were performed. The relative stability of ortho-quinone methides (o-QMs) was calculated, the geometries obtained were compared with the experimentally determined NMR structures, and thereby, the regioselectivity of the reactions has been assigned.}, language = {en} } @article{KleinpeterKoch2021, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Dative or coordinative carbon-boron bond in boron trapped N-heterocyclic carbenes (NHCs)?}, series = {Tetrahedron : the international journal for the rapid publication of full original research papers and critical reviews in organic chemistry}, volume = {80}, journal = {Tetrahedron : the international journal for the rapid publication of full original research papers and critical reviews in organic chemistry}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0040-4020}, doi = {10.1016/j.tet.2020.131787}, pages = {8}, year = {2021}, abstract = {The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of isolated as well as B-C bond length varied model compounds (BR3 trapped NHCs) have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and the results visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values (actually the anisotropy effects measurable in H-1 NMR spectroscopy) are employed to qualify and quantify the present dative vs. coordinative bond character of the boron-carbon bond in the trapped NHCs. Results are confirmed by bond lengths and B-11/C-13 chemical shift variations in the BR3 trapped NHCs.}, language = {en} } @article{KleinpeterKoch2021, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Quantification of sigma-acceptor and pi-donor stabilization in O, S and Hal analogues of N-heterocyclic carbenes (NHCs) on the magnetic criterion}, series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, volume = {125}, journal = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, number = {33}, publisher = {American Chemical Society}, address = {Washington}, issn = {1089-5639}, doi = {10.1021/acs.jpca.1c05257}, pages = {7235 -- 7245}, year = {2021}, abstract = {The spatial magnetic properties, through-space NMR shieldings (TSNMRSs), of stable O, S and Hal analogues of N-heterocyclic carbenes (NHCs) have been calculated using the GIAO perturbation method employing the nucleus-independent chemical shift (NICS) concept and the results visualized as iso-chemical-shielding surfaces (ICSSs) of various sizes and directions. The TSNMRS values (actually the anisotropy effects measurable in H-1 NMR spectroscopy) are employed to qualify and quantify the position of the present mesomeric equilibria (carbenes <-> ylides). The results are confirmed by geometry (bond angles and bond lengths), IR spectra, UV spectra, and C-13 chemical shifts of the electron-deficient carbon centers.}, language = {en} } @article{KleinpeterKoch2021, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Intramolecular carbene stabilization via 3c,2e bonding on basis of the magnetic criterion}, series = {Tetrahedron : the international journal for the rapid publication of full original research papers and critical reviews in organic chemistry}, volume = {95}, journal = {Tetrahedron : the international journal for the rapid publication of full original research papers and critical reviews in organic chemistry}, publisher = {Elsevier Science}, address = {Amsterdam}, issn = {0040-4020}, doi = {10.1016/j.tet.2021.132357}, pages = {9}, year = {2021}, abstract = {The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of bent cyclobutylcarbene 8, 1,2-diboretane-3-ylidene 9, and some carbene analogues of boron 14-18 as most intriguing examples of carbenes, which can be stabilized as homoaromatic systems with 3c,2e bonding, have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and the results visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values (actually, ring current effect/anisotropy effects as measurable in H-1 NMR spectroscopy) are employed to qualify and quantify the degree of present 3c,2e-homoaromaticity. Results are confirmed by geometry (bond angles and bond lengths) and spectroscopic data, the delta(B-11)/ppm data and the C-13 chemical shifts of the carbene electron-deficient centre.}, language = {en} } @article{KleinpeterKoch2020, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Bent Allenes or Di-1,3-betaines-An Answer Given on the Magnetic Criterion}, series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, volume = {124}, journal = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, number = {16}, publisher = {American Chemical Society}, address = {Washington}, issn = {1089-5639}, doi = {10.1021/acs.jpca.0c01392}, pages = {3180 -- 3190}, year = {2020}, abstract = {The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of bent allene 1, the corresponding C-extended 1,3-butadiene derivative 2, and a number of related compounds 3 -20 have been calculated using the gauge-independent atomic orbital perturbation method, employing the nucleus-independent chemical shift concept and visualized as isochemical shielding surfaces of various sizes and directions. Prior to that, both structures and C-13 chemical shifts were calculated and compared with available experimental bond lengths and delta(C-13)/ppm values (also, as a quality criterion for the computed structures). Bond lengths, the delta(C-13)/ppm, and the TSNMRS values are employed to qualify and quantify the electronic structure of the studied compounds in terms of dative or classical electron-sharing bonds.}, language = {en} } @article{KleinpeterKoch2019, author = {Kleinpeter, Erich and Koch, Andreas}, title = {The 13 C chemical shift and the anisotropy effect of the carbene electron-deficient centre}, series = {Magnetic resonance in chemistry}, volume = {58}, journal = {Magnetic resonance in chemistry}, number = {3}, publisher = {Wiley}, address = {Hoboken}, issn = {0749-1581}, doi = {10.1002/mrc.4979}, pages = {280 -- 292}, year = {2019}, abstract = {Both the C-13 chemical shift and the calculated anisotropy effect (spatial magnetic properties) of the electron-deficient centre of stable, crystalline, and structurally characterized carbenes have been employed to unequivocally characterize potential resonance contributors to the present mesomerism (carbene, ylide, betaine, and zwitter ion) and to determine quantitatively the electron deficiency of the corresponding carbene carbon atom. Prior to that, both structures and C-13 chemical shifts were calculated and compared with the experimental delta(C-13)/ppm values and geometry parameters (as a quality criterion for obtained structures).}, language = {en} } @article{KleinpeterKoch2022, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Cyclazines-structure and aromaticity or antiaromaticity on the magnetic criterion}, series = {European journal of organic chemistry}, volume = {2022}, journal = {European journal of organic chemistry}, number = {8}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1434-193X}, doi = {10.1002/ejoc.202101362}, pages = {12}, year = {2022}, abstract = {Structure and spatial magnetic properties, through-space NMR shieldings (TSNMRSs), of all ten cycl[2.2.2]azine to cycl[4.4.4]azine, hetero-analogues and the corresponding hydrocarbons have been calculated at the B3LYP/6-311G(d,p) theory level using the GIAO perturbation method and employing the nucleus independent chemical shift (NICS) concept. The TSNMRS values (actually, the ring current effect as measurable in H-1 NMR spectroscopy) are visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction, and employed to readily qualify and quantify the degree of (anti)aromaticity. Results are confirmed by NMR [delta(H-1)/ppm, delta(N-15)/ppm] and geometry (planar, twisted, bow-shaped) data. The cyclazines N[2.2.2](-) up to N[2.4.4](-) are planar or at most slightly bowl-shaped and, due to coherent peripheral ring currents (except in N[2.3.3](-), N[2.3.4], N[3.3.4](+) and N[2.4.4](+)), develop aromaticity or anti-aromaticity of the whole molecules dependent on the number of peripheral conjugated pi electrons. The cyclazines N[2.3.3](-), N[2.3.4], N[3.3.4](+) and N[2.4.4](+) develop two ring currents of different direction within the same molecule, in which the dominating ring current proves to be paratropic (in N[3.3.4](+) diatropic) including the nodal N p(z) lone pair into the conjugation. The residual cyclazines N[3.4.4], N[4.4.4](-) and N[4.4.4](+) are heavily twisted and, therefore, are not developing peripheral or diverse ring currents. The TSNMRS information about cyclazines and the parent tricyclic annulene analogues is congruent subject to structure and number of peripheral or internal conjugated pi electrons, the corresponding (anti)aromaticity is in unequivocal accordance with Huckel's rule.}, language = {en} } @article{ShainyanBelyakovSigolaevetal.2017, author = {Shainyan, Bagrat A. and Belyakov, Alexander V. and Sigolaev, Yurii F. and Khramov, Alexander N. and Kleinpeter, Erich}, title = {Molecular Structure and Conformational Analysis of 1-Phenyl-1-X-1-Silacyclohexanes (X = F, Cl) by Electron Diffraction, Low-Temperature NMR, and Quantum Chemical Calculations}, series = {The journal of organic chemistry}, volume = {82}, journal = {The journal of organic chemistry}, number = {1}, publisher = {American Chemical Society}, address = {Washington}, issn = {0022-3263}, doi = {10.1021/acs.joc.6b02538}, pages = {461 -- 470}, year = {2017}, abstract = {The molecular structure and conformational preferences of 1-phenyl-1-X-1-silacyclohexanes C5H10Si(Ph,X) (X = F (3), Cl (4)) were studied by gas-phase electron diffraction, low-temperature NMR spectroscopy, and high-level quantum chemical calculations. In the gas phase only three (3) and two (4) stable conformers differing in the axial or equatorial location of the phenyl group and the angle of rotation about the Si-C-ph bond (axi and axo denote the Ph group lying in or out of the X-Si-C-ph plane) contribute to the equilibrium. In 3 the ratio Ph-eq:Ph-axo:Ph-axi is 40(12):55(24):5 and 64:20:16 by experiment and theory, respectively. In 4 the ratio Ph-eq:Ph-axo is 79(15):21(15) and 71:29 by experiment and theory (M06-2X calculations), respectively. The gas-phase electron diffraction parameters are in good agreement with those obtained from theory at the M06-2X/aug-ccPVTZ and MP2/aug-cc-pVTZ levels. Unlike the case for M06-2X, MP2 calculations indicate that 3-Ph-eq conformer lies 0.5 kcal/mol higher than the 3-Ph-axo, conformer. As follows from QTAIM analysis, the phenyl group is more stable when it is located in the axial position but produces destabilization of the silacyclohexane ring: By low temperature NMR spectroscopy the six-membered ring interconversion could be frozen, at 103 K and the present conformational equilibria of 3 and 4 could be determined. The ratio of the conformers is 3-Ph-eq:3-Ph-ax = (75-77):(23-25) and 4-Ph-eq:4-Ph-ax = 82:18.}, language = {en} } @article{KleinpeterKoch2018, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Paramagnetic ring current effects in anti-aromatic structures subject to substitution/annelation quantified by spatial magnetic properties (TSNMRS)}, series = {Tetrahedron}, volume = {74}, journal = {Tetrahedron}, number = {7}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2017.12.020}, pages = {700 -- 710}, year = {2018}, abstract = {The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of the typically anti-aromatic cyclopentadienyl cation, cyclobutadiene, pentalene, s-indacene and of substituted/annelated analogues of the latter structures have been calculated using the CIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values were employed to visualize and quantify the dia(para) magnetic ring current effects in the studied compounds. The interplay of dia(para)magnetic ring current effects due to substitution/annelation caused by heavy exo-cyclic n,pi-electron delocalization can be qualified.}, language = {en} } @article{KirpichenkoShainyanKleinpeteretal.2018, author = {Kirpichenko, Svetlana and Shainyan, Bagrat A. and Kleinpeter, Erich and Shlykov, Sergey A. and Tran Dinh Phien, and Albanov, Alexander}, title = {Synthesis of 3-fluoro-3-methyl-3-silatetrahydropyran and its conformational preferences in gas and solution by GED, NMR and theoretical calculations}, series = {Tetrahedron}, volume = {74}, journal = {Tetrahedron}, number = {15}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2018.02.055}, pages = {1859 -- 1867}, year = {2018}, abstract = {The 3,3-disubstitued 3-silaheterocyclohexane with an electronegative substituent at silicon, 3-fluoro-3-methyl-3-silatetrahydropyran 1, was synthesized, and its molecular structure and conformational properties studied by gas-phase electron diffraction (GED) and low temperature C-13 and F-19 NMR spectroscopy. Quantum-chemical calculations were carried out both for the isolated species and Hcomplexes in gas and in polar medium. The predominance of the 1-FeqMeax conformer (1-F-eq:1-F-ax ratio of 65:35, Delta G degrees = 0.37 kcal/mol) determined from GED is close to the theoretically estimated conformational equilibrium, especially at the DFT level. In solution, low temperature NMR spectroscopy showed no decoalescence of the signals in C-13 (down to 95 K) and F-19 NMR spectra (down to 123 K). However, the calculated F-19 chemical shift of -173.6 ppm for the 1-FeqMeax conformer practically coincides with the experimentally observed value (-173 to -175 ppm) as distinct from that for the 1-FaxMeeq conformer (-188.8 ppm), suggesting compound 1 to be anancomeric in solution, in compliance with its theoretical and experimental preference in the gas phase.}, language = {en} } @article{HansenKochKleinpeter2018, author = {Hansen, Poul Erik and Koch, Andreas and Kleinpeter, Erich}, title = {Ring current and anisotropy effects on OH chemical shifts in resonance-assisted intramolecular H-bonds}, series = {Tetrahedron letters}, volume = {59}, journal = {Tetrahedron letters}, number = {23}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4039}, doi = {10.1016/j.tetlet.2018.05.006}, pages = {2288 -- 2292}, year = {2018}, abstract = {Ring current effects on resonance-assisted and intramolecularly bridged hydrogen bond protons for 10-hydroxybenzo[h]quinoline 1 and a number of related compounds were calculated and the through-space NMR shieldings (TSNMRS) obtained hereby visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. These calculations revealed that this through-space effect is comparably large (up to 2 ppm) dependent on the position of the intramolecularly bridged OH proton, and therefore, contribute considerably to the chemical shift of the latter making it questionable to use delta(OH)/ppm in the estimation of intramolecular hydrogen bond strength without taking this into account. Furthermore, the anisotropy effects of additional groups on the aromatic moiety (e.g. the carbonyl group in salicylaldehyde or in o-hydroxyacetophenone of ca. 0.6 ppm deshielding) should also be considered. These through-space effects need to be taken into account when using OH chemical shifts to estimate hydrogen bond strength.}, language = {en} } @article{KleinpeterKoch2018, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Stable Carbenes or Betaines?}, series = {European journal of organic chemistry}, volume = {2018}, journal = {European journal of organic chemistry}, number = {24}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1434-193X}, doi = {10.1002/ejoc.201800462}, pages = {3114 -- 3121}, year = {2018}, abstract = {The anisotropy effect in H-1 NMR spectroscopy can be readily employed to indicate the position of carbene/betaine mesomeric equilibria. NR2 substituted carbene/betaines tend to adopt betaine structures, whereas in the absence of NR2 substituents, the betaine structures cannot stabilise the structure through both -donation effects of the NMe2 groups and the electronegativity of the nitrogen atoms, and the corresponding carbene-like structures are preferred. These conclusions are supported by calculated bond orders and (C-13)/ppm values. The spatial magnetic properties of isonitriles and carbon monoxide, which can be counted as stable carbenes or, at least, as carbene-analogues, also exist as stable betaine structures, which is again supported by structural and magnetic properties.}, language = {en} } @article{ShainyanSuslovaTranDinhPhienetal.2018, author = {Shainyan, Bagrat A. and Suslova, Elena N. and Tran Dinh Phien, and Shlykov, Sergey A. and Kleinpeter, Erich}, title = {Synthesis, conformational preferences in gas and solution, and molecular gear rotation in 1-(dimethylamino)-1-phenyl-1-silacyclohexane by gas phase electron diffraction (GED), LT NMR and theoretical calculations}, series = {Tetrahedron}, volume = {74}, journal = {Tetrahedron}, number = {32}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2018.06.023}, pages = {4299 -- 4307}, year = {2018}, abstract = {1-(Dimethylamino)-1-phenyl-1-silacyclohexane 1, was synthesized, and its molecular structure and conformational properties studied by gas-phase electron diffraction (GED), low temperature C-13 NMR spectroscopy and quantum-chemical calculations. The predominance of the 1-Ph-ax conformer (1-Ph-eq:1-Ph-ax ratio of 20:80\%, Delta G degrees (317 K) = -0.87 kcal/mol) in the gas phase is close to the theoretically estimated conformational equilibrium. In solution, low temperature NMR spectroscopy showed analyzable decoalescence of C-ipso and C(1,5) carbon signals in C-13 NMR spectra at 103 K. Opposite to the gas state in the freon solution employed (CD2Cl2/CHFCl2/CHFCl2 = 1:1:3), which is still liquid at 100 K, the 1-Ph-eq conformer was found to be the preferred one [(1-Ph-eq: 1-Ph-ax = 77\%: 23\%, K = 77/23 = 2.8; -Delta G degrees = -RT In K (at 103 K) = 0.44 +/- 0.1 kcal/mol]. When comparing 1 with 1-phenyl-1-(X)silacylohexanes (X = H, Me, OMe, F, Cl), studied so far, the trend of predominance of the Ph-ax conformer in the gas phase and of the Ph-eq conformer in solution is confirmed.}, language = {en} } @article{SardarianInalooModarresiAlametal.2019, author = {Sardarian, Ali Reza and Inaloo, Iman Dindarloo and Modarresi-Alam, Ali Reza and Kleinpeter, Erich and Schilde, Uwe}, title = {Metal-Free Regioselective Monocyanation of Hydroxy-, Alkoxy-, and Benzyloxyarenes by Potassium Thiocyanate and Silica Sulfuric Acid as a Cyanating Agent}, series = {The journal of organic chemistry}, volume = {84}, journal = {The journal of organic chemistry}, number = {4}, publisher = {American Chemical Society}, address = {Washington}, issn = {0022-3263}, doi = {10.1021/acs.joc.8b02191}, pages = {1748 -- 1756}, year = {2019}, abstract = {A novel and efficient metal- and solvent-free regioselective para-C-H cyanation of hydroxy-, alkoxy-, and benzyloxyarene derivatives has been introduced, using nontoxic potassium thiocyanate as a cyanating reagent in the presence of silica sulfuric acid (SSA). The desired products are obtained in good to high yields without any toxic byproducts.}, language = {en} } @misc{NeumannHorstkemperKruegeretal.2002, author = {Neumann, Bernhard and Horstkemper, Marianne and Kr{\"u}ger, Wolfgang and Wilkens, Martin and Bohlen, Andreas and Fr{\"u}bing, Peter and Wegener, Michael and Scheff, Ullrich and Neher, Dieter and Brehmer, Ludwig and Kleinpeter, Erich and Wolf, Gunter and Koetz, Joachim and Peter, Martin G. and Senkbeil, Sigrid and Meyer, Till}, title = {Portal = Im Trend: Physiker und Chemiker erforschen "Soft Matter"}, volume = {2002}, issn = {1618-6893}, doi = {10.25932/publishup-50144}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-501441}, pages = {40}, year = {2002}, abstract = {Aus dem Inhalt: Im Trend: Physiker und Chemiker erforschen „Soft Matter" -Brandenburger Netzwerk f{\"u}r Existenzgr{\"u}nder erh{\"a}lt F{\"o}rderung -Universit{\"a}t leistet Beitrag zum Romantik-Jahr -Musiksender MTV und Bryan Adams auf dem Campus}, language = {de} } @article{KleinpeterKoch2019, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Is the term "Carbene" justified for remote N-heterocyclic carbenes (r-NHCs) and abnormal N-heterocyclic carbenes (aNHCs/MICs)?}, series = {Tetrahedron}, volume = {75}, journal = {Tetrahedron}, number = {11}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2019.02.005}, pages = {1548 -- 1554}, year = {2019}, abstract = {The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of typical N-heterocyclic carbenes NHCs, r-NHCs, a-NHCs and MICs have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. Prior to that both structures and 13C chemical shifts were calculated and in case of isolated carbenes the computed δ(13C)/ppm values compared (as a quality criterion for obtained structures) with the experimental ones. The TSNMRS values of the studied carbenes, which are in mesomeric equilibrium with zwitterionic (ylide/betaine/mesoionic) resonance contributors, are employed to qualify and quantify the present electronic structure and if the term carbene is still justified to denote the compounds studied. The results, thus obtained from spatial magnetic properties (TSNMRS), are compared with the geometry of the compounds, the corresponding WIBERG's bond index values, and the 13C chemical shifts especially of the carbene electron-deficient centre.}, language = {en} } @article{ShainyanKleinpeterSuslova2019, author = {Shainyan, Bagrat A. and Kleinpeter, Erich and Suslova, E. N.}, title = {Conformational Analysis of (1,1′-Phenyl-1,1′-silacyclohex-1-yl)disiloxane}, series = {Russian journal of general chemistry}, volume = {89}, journal = {Russian journal of general chemistry}, number = {4}, publisher = {Pleiades Publ.}, address = {New York}, issn = {1070-3632}, doi = {10.1134/S1070363219040121}, pages = {713 -- 716}, year = {2019}, abstract = {The DFT and MP2 theoretical conformational analysis of the recently synthesized (1,1-phenyl-1,1-silacyclohex-1-yl)disiloxane has revealed the energetic preference of the Ph-ax,Ph-ax conformer. The Ph-ax,Ph-ax: Ph-ax,Ph-eq: Ph-eq,Ph-eq conformers ratio has been estimated as of 46.6: 33.1: 20.3 from the M062X/6-311G(d,p) free energy simulation, suggesting the possibility of detecting individual conformers experimentally, e.g., by low-temperature H-1 and C-13 NMR spectroscopy. However, only the presence of several conformers has been detected by means of H-1 NMR spectroscopy at 113 K; determination of the (Hz) and G(\#) (kcal/mol) parameters for the 6-membered ring interconversion has been impossible due to the signals broadening at low temperature, signal temperature shifts, and extremely low barrier of ring inversion at T-c < 113 K.}, language = {en} } @article{KleinpeterKoch2019, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Benzenium Ion}, series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, volume = {123}, journal = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, number = {20}, publisher = {American Chemical Society}, address = {Washington}, issn = {1089-5639}, doi = {10.1021/acs.jpca.9b03121}, pages = {4443 -- 4451}, year = {2019}, abstract = {The spatial magnetic properties, through-space NMR shieldings (TSNMRSs), of the benzenium cation (C6H7+) 1 and of +/- I/M-substituted analogues C6H6X+ 3-8 [X = -Me, -CF3, -NH2, -NO2, -NO, -SiH3] have been calculated using the gauge-independent atomic orbital perturbation method employing the nucleus-independent chemical shift concept, and iso-chemical-shielding surfaces of various sizes and directions have been observed. The TSNMRS values were employed to compare the spatial magnetic properties (TSNMRS) of benzene and the benzenium ion 1 and then further compared with analogues 3-8, to answer the question whether the electronic structures of 1 and 3-8 are still similar to those of aromatic species or somewhat similar to the antiaromatic cyclopentadienyl cation 2, supported by structural data and delta(C-13)/ppm values.}, language = {en} } @misc{KleinpeterShainyan2019, author = {Kleinpeter, Erich and Shainyan, Bagrat A.}, title = {Very low-temperature dynamic Si-29 NMR study of the conformational equilibrium of (1,1-phenyl-1,1-silacyclohex-1-yl)disiloxane}, series = {Magnetic resonance in chemistry}, volume = {57}, journal = {Magnetic resonance in chemistry}, number = {6}, publisher = {Wiley}, address = {Hoboken}, issn = {0749-1581}, doi = {10.1002/mrc.4870}, pages = {317 -- 319}, year = {2019}, language = {en} } @article{SzatmariBelasriHeydenreichetal.2019, author = {Szatmari, Istvan and Belasri, Khadija and Heydenreich, Matthias and Koch, Andreas and Kleinpeter, Erich and Fulop, Ferenc}, title = {Ortho-Quinone methide driven synthesis of new O,N- or N,N-Heterocycles}, series = {ChemistryOpen : including thesis treasury}, volume = {8}, journal = {ChemistryOpen : including thesis treasury}, number = {7}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {2191-1363}, doi = {10.1002/open.201900150}, pages = {961 -- 971}, year = {2019}, abstract = {To synthesize functionalized Mannich bases that can serve two different types of ortho-quinone methide (o-QM) intermediates, 2-naphthol and 6-hydroxyquinoline were reacted with salicylic aldehyde in the presence of morpholine. The Mannich bases that can form o-QM and aza-o-QM were also synthesized by mixing 2-naphthol, 2-nitrobenzaldehyde, and morpholine followed by reduction of the nitro group. The highly functionalized aminonaphthol derivatives were then tested in [4+2] cycloaddition with different cyclic imines. The reaction proved to be both regio- and diastereoselective. In all cases, only one reaction product was obtained. Detailed structural analyses of the new polyheterocycles as well as conformational studies including DFT modelling were performed. The relative stability of o-QMs/aza-o-QM were also calculated, and the regioselectivity of the reactions could be explained only when the cycloaddition started from aminodiol 4. It was summarized that starting from diaminonaphthol 25, the regioselectivity of the reaction is driven by the higher nucleophilicity of the amino group compared with the hydroxy group. 12H-benzo[a]xanthen-12-one (11), formed via o-QM formation, was isolated as a side product. The proton NMR spectrum of 11 proved to be very unique from NMR point of view. The reason for the extreme low-field position of proton H-1 could be accounted for by theoretical calculation of structure and spatial magnetic properties of the compound in combination of ring current effects of the aromatic moieties and steric compression within the heavily hindered H(1)-C(1)-C(12b)-C(12a)-C(12)=O structural fragment.}, language = {en} } @article{KleinpeterKoch2019, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Benzyne - an acetylene- or cumulene-like electronic structure?}, series = {Tetrahedron}, volume = {75}, journal = {Tetrahedron}, number = {33}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2019.07.011}, pages = {4663 -- 4668}, year = {2019}, abstract = {The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of benzyne 1 and analogues (benzene 2, 1,2,3-cyclohexatriene 3, cyclohexen-3-yne 4, cyclohexen-4-yne 5, cyclohexyne 6) have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values could be employed to compare the diatropic ring current effects of benzene and benzyne, and, when compared with the spatial magnetic properties of the analogues, to answer the question whether the benzyne electronic structure is more acetylene- or cumulene-like, supported by structural data and delta(C-13)/ppm values. (C) 2019 Published by Elsevier Ltd.}, language = {en} } @article{ShainyanSuslovaTranDinhPhienetal.2019, author = {Shainyan, Bagrat A. and Suslova, Elena N. and Tran Dinh Phien, and Shlykov, Sergey A. and Heydenreich, Matthias and Kleinpeter, Erich}, title = {1-Methylthio-1-phenyl-1-silacyclohexane: Synthesis, conformational preferences in gas and solution by GED, NMR and theoretical calculations}, series = {Tetrahedron}, volume = {75}, journal = {Tetrahedron}, number = {46}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2019.130677}, pages = {9}, year = {2019}, abstract = {1-Methylthio-1-phenyl-1-silacyclohexane 1, the first silacyclohexane with the sulfur atom at silicon, was synthesized and its molecular structure and conformational preferences studied by gas-phase electron diffraction (GED) and low temperature C-13 and Si-29 NMR spectroscopy (LT NMR). Quantum-chemical calculations were carried out both for the isolated species and solvate complexes in gas and in polar medium. The predominance of the 1-MeSaxPheq conformer in gas phase (1-Ph-eq :1-Ph-ax = 55:45, Delta G degrees = 0.13 kcal/mol) determined from GED is consistent with that measured in the freon solution by LT NMR (1-Ph-eq:1-Ph-ax = 65:35, Delta G degrees = 0.12 kcal/mol), the experimentally measured ratios being close to that estimated by quantum chemical calculations at both the DFT and MP2 levels of theory. (C) 2019 Elsevier Ltd. All rights reserved.}, language = {en} } @article{MovahedifarModarresiAlamKleinpeteretal.2017, author = {Movahedifar, Fahimeh and Modarresi-Alam, Ali Reza and Kleinpeter, Erich and Schilde, Uwe}, title = {Dynamic H-1-NMR study of unusually high barrier to rotation about the partial C-N double bond in N,N-dimethyl carbamoyl 5-aryloxytetrazoles}, series = {Journal of molecular structure}, volume = {1133}, journal = {Journal of molecular structure}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0022-2860}, doi = {10.1016/j.molstruc.2016.12.010}, pages = {244 -- 252}, year = {2017}, abstract = {The synthesis of new N,N-dimethyl carbamoyl 5-aryloxytetrazoles have been reported. Their dynamic H-1-NMR via rotation about C-N bonds in moiety of urea group [a; CO-NMe2 and b; (2-tetrazolyl)N-CO rotations] in the solvents CDCl3 (223-333 K) and DMSO (298-363 K) is studied. Accordingly, the free energies of activation, obtained 16.5 and 16.9 kcal mol(-1) respectively, attributed to the conformational isomerization about the Me2N-C=O bond (a rotation). Moreover, a and b barrier to rotations in 5-((4-methylphenoxy)-N,N-dimethyl-2H-tetrazole-2-carboxamide (P) also were computed at level of B3LYP using 6-311++G** basis set. The optimized geometry parameters are in good agreement with X-ray structure data. The computation of energy barrier for a and b was determined 16.9 and 2.5 kcal mol(-1), respectively. The former is completely in agreement with the result obtained via dynamic NMR. X-ray structure analysis data demonstrate that just 2-acylated tetrazole was formed in the case of 5-(p-tolyloxy)-N,N-dimethyl-2H-tetrazole-2-carboxamide. X-ray data also revealed a planar trigonal orientation of the Me2N group which is coplanar to carbonyl group with the partial double-bond C-N character. It also demonstrates the synperiplanar position of C=O group with tetrazolyl ring. On average, in solution the plane containing carbonyl bond is almost perpendicular to the plane of the tetrazolyl ring (because of steric effects as confirmed by B3LY12/6-311++G**) while the plane containing Me2N group is coplanar with carbonyl bond which is in contrast with similar urea derivatives and it demonstrates the unusually high rotational energy barrier of these compounds. (C) 2016 Elsevier B.V. All rights reserved.}, language = {en} } @article{KleinpeterWernerLinker2017, author = {Kleinpeter, Erich and Werner, Peter and Linker, Torsten}, title = {Synthesis and NMR spectroscopic conformational analysis of benzoic acid esters of mono- and 1,4-dihydroxycyclohexane, 4-hydroxycyclohexanone and the -ene analogue - The more polar the molecule the more stable the axial conformer}, series = {Tetrahedron}, volume = {73}, journal = {Tetrahedron}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2017.04.029}, pages = {3801 -- 3809}, year = {2017}, abstract = {para-Substituted benzoic acid esters of cyclohexanol, 1,4-dihydroxycyclohexane, 4-hydroxy-cyclohexanone and of the corresponding exo-methylene derivative were synthesized and the conformational equilibria of the cyclohexane skeleton studied by low temperature H-1 and C-13 NMR spectroscopy. The geometry optimized structures of the axial/equatorial chair conformers were computed at the DFT level of theory. Only one preferred conformation of the ester group was obtained for both the axial and the equatorial conformer, respectively. The content of the axial conformer increases with growing polarity of the 6-membered ring moiety; hereby, in addition, the effect of sp(2) hybridization/polarity of C(4)= O/C(4)= CH2 on the present conformational equilibria is critically evaluated. Another dynamic process could be studied, for the first time in this kind of compounds. (C) 2017 Elsevier Ltd. All rights reserved.}, language = {en} } @article{KleinpeterKoch2017, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Identification of mesomeric substructures by through-space NMR shieldings (TSNMRS). Trimethine cyanine/merocyanine-like or aromatic pi-electron delocalization?}, series = {Tetrahedron}, volume = {73}, journal = {Tetrahedron}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2017.05.062}, pages = {4265 -- 4274}, year = {2017}, abstract = {The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of amino-substituted heteraromatic six-membered ring systems such as pyrylium/thiopyrylium analogues have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values were employed to quantify and visualize the existing aromaticity of the studied compounds. Due to strong conjugation of six-membered ring pi-electrons and lone pairs of the exo-cyclic amino substituents (restricted rotation about partial C,N double bonds) the interplay of still aromatic and already dominating trimethine cyanine/merocyanine-like substructures can be estimated. (C) 2017 Elsevier Ltd. All rights reserved.}, language = {en} } @article{KleinpeterHeydenreichKochetal.2017, author = {Kleinpeter, Erich and Heydenreich, Matthias and Koch, Andreas and Krtitschka, Angela and Kr{\"u}ger, Tobias and Linker, Torsten}, title = {NMR spectroscopic conformational analysis of 4-methylene-cyclohexyl pivalateThe effect of sp(2) hybridization}, series = {Magnetic resonance in chemistry}, volume = {55}, journal = {Magnetic resonance in chemistry}, publisher = {Wiley}, address = {Hoboken}, issn = {0749-1581}, doi = {10.1002/mrc.4630}, pages = {1073 -- 1078}, year = {2017}, abstract = {The conformational equilibrium of the axial/equatorial conformers of 4-methylene-cyclohexyl pivalate is studied by dynamic NMR spectroscopy in a methylene chloride/freon mixture. At 153K, the ring interconversion gets slow on the nuclear magnetic resonance timescale, the conformational equilibrium (-G degrees) can be examined, and the barrier to ring interconversion (G(\#)) can be determined. The structural influence of sp(2) hybridization on both G degrees and G(\#) of the cyclohexyl moiety can be quantified.}, language = {en} } @article{ShainyanKirpichenkoKleinpeter2017, author = {Shainyan, Bagrat A. and Kirpichenko, Svetlana V. and Kleinpeter, Erich}, title = {Conformational Preferences of the Phenyl Group in 1-Phenyl-1-X-1-silacyclo-hexanes (X = MeO, HO) and 3-Phenyl-3-X-3-silatetrahydropyrans (X = HO, H) by Low Temperature C-13 NMR Spectroscopy and Theoretical Calculations}, series = {The journal of organic chemistry}, volume = {82}, journal = {The journal of organic chemistry}, publisher = {American Chemical Society}, address = {Washington}, issn = {0022-3263}, doi = {10.1021/acs.joc.7b02505}, pages = {13414 -- 13422}, year = {2017}, abstract = {New Si-phenyl-substituted silacyclohexanes and 3-silatetrahydropyrans have been synthesized and studied with respect to the conformational equilibria of the heterosix-membered ring by low temperature C-13 NMR spectroscopy and quantum chemical calculations. For 1-methoxy-1-phenylsilacyclohexane 1 and 3-phenyl-3-silatetrahydropyran 4 the conformational equilibria could be frozen and assigned. The Ph-ax reversible arrow Ph-eq equilibrium constants at 103 K are 2.21 for 1 and 4.59 for 4. In complete agreement with former studies of similar silicon compounds, molecules 1 and 4 prefer to adopt the Pheq conformation. The conformational equilibria of 1-hydroxy-1-phenylsilacydohexane 2 and 3-hydroxy-3-phenyl-3-silatetrahydropyran 3 could not be frozen at 100 K and proved to be heavily one-sided (if not anancomeric). Obviously, there is a general trend of predominance of Phax conformer in the gas phase and of Pheq in solution. For the isolated molecules of silanols 2 and 3, calculations allowed to explain the axial predominance of the phenyl group by a larger polarization of the Si-Ph than of the Si-O bond in the Phax conformer and additional destabilization of 3-Ph-eq conformer by repulsion of unidirectional dipoles of the endocyclic oxygen lone pair and of the highly polar axial Si-O bond.}, language = {en} } @article{KleinpeterKoch2016, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Y-aromaticity - existing: yes or no? An answer given on the magnetic criterion (TSNMRS)}, series = {Tetrahedron}, volume = {72}, journal = {Tetrahedron}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2016.02.020}, pages = {1675 -- 1685}, year = {2016}, abstract = {The spatial magnetic properties (Through Space NMR Shieldings - TSNMRS) of a number of Y-shaped structures possessing 4n+2 pi-electrons (i.a. the trimethylenemethane ions TMM2+, TMM2-, the guanidinium cation, substituted and hetero analogues) have been computed, visualized as Isochemical Shielding Surfaces (ICSS) of various size and direction, were examined subject to present Y-aromaticity and the results compared with energetic and geometric criteria obtained already. (C) 2016 Elsevier Ltd. All rights reserved.}, language = {en} } @article{BartaSzatmariFueloepetal.2016, author = {Barta, Petra and Szatmari, Istvan and Fueloep, Ferenc and Heydenreich, Matthias and Koch, Andreas and Kleinpeter, Erich}, title = {Synthesis and stereochemistry of new naphth[1,3]oxazino[3,2-a] benzazepine and naphth[1,3]oxazino[3,2-e]thienopyridine derivatives}, series = {Tetrahedron}, volume = {72}, journal = {Tetrahedron}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2016.03.058}, pages = {2402 -- 2410}, year = {2016}, abstract = {Through the reactions of 1- or 2-naphthol and 4,5-dihydro-3H-benz[c]azepine or 6,7-dihydrothieno[3,2-c]pyridine, new aminonaphthol derivatives were prepared. The syntheses were extended by using N-containing naphthol analogues such as 5-hydroxyisoquinoline and 6-hydroxyquinoline. The ring closures of the novel bifunctional compounds were also achieved, resulting in new naphth[2,1-e][1,3]oxazines, naphth[1,2-e][1,3]oxazines, isoquinolino[5,6-e][1,3]oxazines and quinolino[5,6-e][1,3]oxazines. H-1 NMR spectra of the target heterocycles 16, 20 and 21 were sufficiently resolved to indentify the present stereochemistry; therefore, beside computed structures, spatial experimental (dipolar coupling-NOE) and computed (ring current effect of the naphthyl moiety-TSNMRS) NMR studies were employed. The studied heterocycles exist exclusively as S(14b),R(N), R(14b),S(N), and S(16b)S(N) isomers, respectively. The flexible moieties of the studied compounds prefer. (C) 2016 Elsevier Ltd. All rights reserved.}, language = {en} } @article{RasovicBlagojevicBaranacStojanovicetal.2016, author = {Rasovic, Aleksandar and Blagojevic, Vladimir and Baranac-Stojanovic, Marija and Kleinpeter, Erich and Markovic, Rade and Minic, Dragica M.}, title = {Quantification of the push-pull effect in 2-alkylidene-4-oxothiazolidines by using NMR spectral data and barriers to rotation around the C=C bond}, series = {New journal of chemistry}, volume = {40}, journal = {New journal of chemistry}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1144-0546}, doi = {10.1039/c6nj00901h}, pages = {6364 -- 6373}, year = {2016}, abstract = {Information about the strength of donor-acceptor interactions in push-pull alkenes is valuable, as this so-called "push-pull effect' influences their chemical reactivity and dynamic behaviour. In this paper, we discuss the applicability of NMR spectral data and barriers to rotation around the CQC double bond to quantify the push-pull effect in biologically important 2-alkylidene-4-oxothiazolidines. While olefinic proton chemical shifts and differences in C-13 NMR chemical shifts of the two carbons constituting the CQC double bond fail to give the correct trend in the electron withdrawing ability of the substituents attached to the exocyclic carbon of the double bond, barriers to rotation prove to be a reliable quantity in providing information about the extent of donor-acceptor interactions in the push-pull systems studied. In particular all relevant kinetic data, that is the Arrhenius parameters ( apparent activation energy Ea and frequency factor A) and activation parameters ( Delta S-double dagger, Delta H-double dagger and Delta G(double dagger)), were determined from the data of the experimentally studied configurational isomerization of ( E)-9a. These results were compared to previously published related data for other two compounds, ( Z)-1b and ( 2E, 5Z)-7, showing that experimentally determined Delta G(double dagger) values are a good indicator of the strength of push-pull character. Theoretical calculations of the rotational barriers of eight selected derivatives excellently correlate with the calculated CQC bond lengths and corroborate the applicability of Delta G(double dagger) for estimation of the strength of the push-pull effect in these and related systems.}, language = {en} } @article{BalciAkkayaAkyuzetal.2016, author = {Balci, K. and Akkaya, Y. and Akyuz, S. and Collier, W. B. and Stricker, M. C. and Stover, D. D. and Ritzhaupt, G. and Koch, Andreas and Kleinpeter, Erich}, title = {The effects of conformation and zwitterionic tautomerism on the structural and vibrational spectral data of anserine}, series = {Vibrational spectroscopy : an international journal devoted to applications of infrared and raman spectroscopy}, volume = {86}, journal = {Vibrational spectroscopy : an international journal devoted to applications of infrared and raman spectroscopy}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0924-2031}, doi = {10.1016/j.vibspec.2016.08.003}, pages = {277 -- 289}, year = {2016}, abstract = {In this study, the stable conformers of neutral anserine were searched by molecular dynamics simulations and energy minimization calculations using the MM2 force field. Thermochemical calculations at B3LYP/6-31G(d) level of theory followed these preliminary calculations. The results confirmed that neutral anserine has quite a flexible structure and many stable gauche and trans conformers at room temperature. Nevertheless, two are considerably more favourable in energy than the others and expected to dominate the gas-phase and matrix IR spectra of the molecule. The corresponding structural and vibrational spectral data for these two conformers of neutral anserine, whose relative stabilities were also examined by high-accuracy energy calculations carried out using G3MP2B3 method, and for the most stable conformer of anserine in zwitterion form were calculated at B3LYP/6-311++G(d,p) level of theory. The calculated harmonic force constants were refined using the Scaled Quantum Mechanical Force Field (SQM-FF) method and then used to produce the refined wavenumbers, potential energy distributions (PEDs) and IR and Raman intensities. These refined data together with the scaled harmonic wavenumbers obtained using another method, Dual Scale factors (DS), enabled us to correctly analyse the observed IR and Raman spectra of anserine and revealed the effects of conformation and zwitterionic tautomerism on its structural and vibrational spectral data. (C) 2016 Elsevier B.V. All rights reserved.}, language = {en} } @article{WentrupKochKleinpeter2016, author = {Wentrup, Curt and Koch, Rainer and Kleinpeter, Erich}, title = {Twisted C=C Double Bonds with Very Low Rotational Barriers in Dioxanediones and Isoxazolones Determined by Low-Temperature Dynamic NMR Spectroscopy and Computational Chemistry}, series = {European journal of organic chemistry}, journal = {European journal of organic chemistry}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1434-193X}, doi = {10.1002/ejoc.201600931}, pages = {4985 -- 4990}, year = {2016}, language = {en} } @misc{RasovicBlagojevicBaranacStojanovicetal.2016, author = {Rasovic, Aleksandar and Blagojevic, Vladimir and Baranac-Stojanovic, Marija and Kleinpeter, Erich and Markovic, Rade and Minic, Dragica M.}, title = {Quantification of the push-pull effect in 2-alkylidene-4-oxothiazolidines by using NMR spectral data and barriers to rotation around the C=C bond}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-394523}, pages = {6364 -- 6373}, year = {2016}, abstract = {Information about the strength of donor-acceptor interactions in push-pull alkenes is valuable, as this so-called "push-pull effect" influences their chemical reactivity and dynamic behaviour. In this paper, we discuss the applicability of NMR spectral data and barriers to rotation around the C[double bond, length as m-dash]C double bond to quantify the push-pull effect in biologically important 2-alkylidene-4-oxothiazolidines. While olefinic proton chemical shifts and differences in 13C NMR chemical shifts of the two carbons constituting the C[double bond, length as m-dash]C double bond fail to give the correct trend in the electron withdrawing ability of the substituents attached to the exocyclic carbon of the double bond, barriers to rotation prove to be a reliable quantity in providing information about the extent of donor-acceptor interactions in the push-pull systems studied. In particular all relevant kinetic data, that is the Arrhenius parameters (apparent activation energy Ea and frequency factor A) and activation parameters (ΔS‡, ΔH‡ and ΔG‡), were determined from the data of the experimentally studied configurational isomerization of (E)-9a. These results were compared to previously published related data for other two compounds, (Z)-1b and (2E,5Z)-7, showing that experimentally determined ΔG‡ values are a good indicator of the strength of push-pull character. Theoretical calculations of the rotational barriers of eight selected derivatives excellently correlate with the calculated C[double bond, length as m-dash]C bond lengths and corroborate the applicability of ΔG‡ for estimation of the strength of the push-pull effect in these and related systems.}, language = {en} } @article{BauerHartmannKleinpeteretal.2015, author = {Bauer, Monika and Hartmann, Lutz and Kleinpeter, Erich and Kuschel, Frank and Pithart, Cornelia and Weissflog, Wolfgang}, title = {Chiral Dopants Derived from Ephedrine/Pseudoephedrine: Structure and Medium Effects on the Helical Twisting Power}, series = {Molecular crystals and liquid crystals}, volume = {608}, journal = {Molecular crystals and liquid crystals}, number = {1}, publisher = {Routledge, Taylor \& Francis Group}, address = {Abingdon}, issn = {1542-1406}, doi = {10.1080/15421406.2014.949592}, pages = {14 -- 24}, year = {2015}, abstract = {Chiral dopants were obtained by acylation of enantiomerically pure ephedrine and pseudoephedrine with promesogenic carbonyl reagents. The products have been investigated with respect to their chiral transfer ability on nematic host matrices characterized by extreme differences of the dielectric anisotropy. It has been found that the medium dependence of the helicity induction nearly disappears at reduced temperatures. Based on variable temperature H-1 NMR studies on monoacylated homologues, the estimated coalescence temperatures and free activation enthalpies for the hindered rotation around C-N bonds could be correlated with the helical twisting power. Measurements by dielectric spectroscopy reveal the correlation between the molar mass of substituents linked to the chiral building block and the dynamic glass transition of corresponding chiral dopants. Furthermore, the effect of intramolecular and intermolecular hydrogen bonds has been studied by ATR-FTIR spectroscopy.}, language = {en} } @article{KleinpeterMichaelisKoch2015, author = {Kleinpeter, Erich and Michaelis, Marcus and Koch, Andreas}, title = {Are para-nitro-pyridine N-oxides quinonoid or benzenoid? An answer given by spatial NICS (TSNMRS)}, series = {Tetrahedron}, volume = {71}, journal = {Tetrahedron}, number = {15}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2015.02.043}, pages = {2273 -- 2279}, year = {2015}, abstract = {The spatial magnetic properties (Through-Space NMR Shieldings-TSNMRS) of a number of substituted para-nitro-pyridine N-oxides have been computed, visualized as Iso-Chemical-Shielding-Surfaces (ICSS) of various size and direction, and were examined subject to the present quinonoid or benzenoid pi-relectron distribution of the six-membered ring. (C) 2015 Elsevier Ltd. All rights reserved.}, language = {en} } @article{KolocourisKochKleinpeteretal.2015, author = {Kolocouris, Antonios and Koch, Andreas and Kleinpeter, Erich and Stylianakis, Ioannis}, title = {2-Substituted and 2,2-disubstituted adamantane derivatives as models for studying substituent chemical shifts and C-H-ax center dot center dot center dot Y-ax cyclohexane contacts-results from experimental and theoretical NMR spectroscopic chemical shifts and DFT structures}, series = {Tetrahedron}, volume = {71}, journal = {Tetrahedron}, number = {16}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2015.01.044}, pages = {2463 -- 2481}, year = {2015}, abstract = {The complete H-1 and C-13 NMR chemical shifts assignment for various 2-substituted and 2,2-disubstituted adamantane derivatives 1-38 in CDCl3 solution was realized on the basis of NMR experiments combined with chemical structure information and DFT-GIAO (B3LYP/6-31+G(d,p)-GIAO) calculations of chemical shifts in solution. Substituent-induced C-13 NMR chemical shifts (SCS) are discussed. C-H-ax center dot center dot center dot Y-ax contacts are a textbook prototype of steric hindrance in organic chemistry. The nature of these contacts will be further investigated in this work on basis of new adamantane derivatives, which are substituted at C-2 to provide models for 1,4-C-H-ax center dot center dot center dot Y-ax and 1,5-C-H-ax center dot center dot center dot Y-ax contacts. The B3LYP/6-31+G(d,p) calculations predicted the presence of NBO hyperconjugative attractive interactions between C-H-ax and Y-ax groups along C-H-ax center dot center dot center dot Y-ax contacts. The H-1 NMR signal separation, Delta delta(gamma-CH2), reflects the strength of the H-bonded C-H-ax center dot center dot center dot Y-ax contact. (C) 2015 Elsevier Ltd. All rights reserved.}, language = {en} } @article{KleinpeterKriigerKoch2015, author = {Kleinpeter, Erich and Kriiger, Stefanie and Koch, Andreas}, title = {Anisotropy Effect of Three-Membered Rings in H-1 NMR Spectra: Quantification by TSNMRS and Assignment of the Stereochemistry}, series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, volume = {119}, journal = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, number = {18}, publisher = {American Chemical Society}, address = {Washington}, issn = {1089-5639}, doi = {10.1021/acs.jpca.5b03078}, pages = {4268 -- 4276}, year = {2015}, abstract = {The spatial magnetic properties (through Space NAIR shieldings, TSNMRSs) of cyclopropane; of the heteroanalogous oxirane, thiirane, and aziridine; and of various substituted dis-, and tris-cyclic analogues have been computed by the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept and visualized as iso-chemical-shielding surfaces (ICSSs) of various size and direction. The TSNMRS values, thus obtained, can be employed to visualize the anisotropy (ring current) effect of I the cyclopropane ring moiety. This approach has been employed to qualify and quantify substituent influences and contributions of appropriate ring heteroatoms O, NH, and S on the anisotropy (ring current) effect of three-mernbered ring moieties, and to assign the stereochemistry of mono-, bis-, and tris cyclic structures containing cyclopropane as a structural element. Characteristic examples are included.}, language = {en} } @article{ShainyanKirpichenkoKleinpeteretal.2015, author = {Shainyan, Bagrat A. and Kirpichenko, Svetlana V. and Kleinpeter, Erich and Shlykov, Sergey A. and Osadchiy, Dmitriy Yu.}, title = {Molecular structure and conformational analysis of 3-methyl-3-phenyl-3-silatetrahydropyran. Gas-phase electron diffraction, low temperature NMR and quantum chemical calculations}, series = {Tetrahedron}, volume = {71}, journal = {Tetrahedron}, number = {23}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2015.03.117}, pages = {3810 -- 3818}, year = {2015}, abstract = {The molecular structure and conformational behavior of 3-methyl-3-phenyl-3-silatetrahydropyran 1 was studied by gas-phase electron diffraction (GED-MS), low temperature C-13 NMR spectroscopy (LT NMR) and theoretical calculations. The 1-Ph-eq and 1-Ph-ax conformers were located on the potential energy surface. Rotation about the Si-C-ph bond revealed the phenyl ring orthogonal to the averaged plane of the silatetrahydropyran ring for 1-Ph-eq and a twisted orientation for 1-Ph-ax. Theoretical calculations and GED analysis indicate the predominance of 1-Ph-ax in the gas phase with the ratio of conformers (GED) 1-Ph-eq:1-Ph-ax=38:62 (Delta G degrees(307)=-0.29 kcal/mol). In solution, LT NMR spectroscopy gives almost the opposite ratio Ph-eq:1-Ph-ax=68:32 (Delta G degrees(103)=0.16 kcal/mol). Simulation of solvent effects using the PCM continuum model or by calculation of the solvent-solute complexes allowed us to rationalize the experimentally observed opposite conformational predominance of the conformers of compound 1 in the gas phase and in solution. (C) 2015 Elsevier Ltd. All rights reserved.}, language = {en} } @article{KleinpeterKoch2015, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Characterization and quantification of quasi-aromaticity by spatial magnetic properties (TSNMRS)}, series = {Tetrahedron}, volume = {71}, journal = {Tetrahedron}, number = {33}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2015.06.019}, pages = {5275 -- 5284}, year = {2015}, abstract = {The spatial magnetic properties (Through Space NMR Shieldings-TSNMRS) of various types of structures with suggested quasi-aromaticity (a summaring topic: in detail push pull, captodative, chelate, supramolecular aromaticity, etc.) have been computed, are visualized as Isochemical Shielding Surfaces (ICSS) of various size/direction and examined subject to identify and quantify present (partial) aromaticity. While the TSNMRS approach proves really helpful [even in cases of (4n+2) pi-electron cyclic moieties formed via non-covalent polar interactions] quasi-aromaticity suggested for enol forms of 1,3-dicarbonyl compounds via resonance-assisted intramolecular and intermolecular hydrogen bonding cannot be confirmed. (C) 2015 Elsevier Ltd. All rights reserved.}, language = {en} } @article{ShainyanKirpichenkoKleinpeter2015, author = {Shainyan, Bagrat A. and Kirpichenko, Svetlana V. and Kleinpeter, Erich}, title = {Stereochemistry of 3-isopropoxy-3-methyl-1,3-oxasilinane-the first 3-silatetrahydropyran with an exo-cyclic RO-Si bond}, series = {Tetrahedron}, volume = {71}, journal = {Tetrahedron}, number = {38}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2015.07.047}, pages = {6720 -- 6726}, year = {2015}, abstract = {Molecular structure and conformational behavior of 3-isopropoxy-3-methyl-3-oxasilinane is studied by low temperature C-13 NMR spectroscopy and theoretical calculations (DFT, MP2). Two conformers, 1-ROax and 1-ROeq, were found experimentally and located on the potential energy surface. LT C-13 NMR spectroscopy gives almost equal population of the two conformers at 98 K with Delta G(98K)degrees=0.02 kcal/mol in favor of 1-ROax and Delta G(98K)(\#)=4.5 kcal/mol. The corresponding DFT calculated values (Delta G(98K)degrees=0.03 kcal/mol, Delta G(98K)(\#)=5.1 kcal/mol) are in excellent agreement with the experiment. Detailed DFT and MP2 calculations of the solvent effect on the conformational equilibrium were performed and highlighted the leveling out of the two conformers when transferred from gas to solution. (C) 2015 Published by Elsevier Ltd.}, language = {en} } @article{ShainyanKirpichenkoChipaninaetal.2015, author = {Shainyan, Bagrat A. and Kirpichenko, Svetlana V. and Chipanina, Nina N. and Oznobikhina, Larisa P. and Kleinpeter, Erich and Shlykov, Sergey A. and Osadchiy, Dmitriy Yu.}, title = {Synthesis and Conformational Analysis of 3-Methyl-3-silatetrahydropyran by GED, FTIR, NMR, and Theoretical Calculations: Comparative Analysis of 1-Hetero-3-methyl-3-silacyclohexanes}, series = {The journal of organic chemistry}, volume = {80}, journal = {The journal of organic chemistry}, number = {24}, publisher = {American Chemical Society}, address = {Washington}, issn = {0022-3263}, doi = {10.1021/acs.joc.5b02355}, pages = {12492 -- 12500}, year = {2015}, abstract = {3-Methyl-3-silatetrahydropyran 1 was synthesized and its molecular structure and conformational behavior was studied by gas-phase electron diffraction (GED), FTIR, low temperature H-1 and C-13 NMR spectroscopy, and by theoretical calculations (DFT, MP2). Two conformers; 1-ax and 1-eq; were located on the potential energy Surface. In the gas phase; a slight predominance of the axial conformer was determined, with the ratio 1-ax:1-eq = 54(9):46(9) (from GED) or 53:47 or 61;39 (from IR). In solution, LT NMR spectroscopy at 103 K gives the ratio 1-ax:1-eq = 35:65 (-Delta G(103)degrees = 0.13 kcal/mol). Simulation of solvent effects using the PCM continuum model or by calculation of the corresponding solvent-solute complexes allowed us to rationalize the experimentally observed opposite conformational predominance of the conformers of 3-methyl-3-silatettahydropyran in the gas phase and in solution. Comparative analysis of the effect of heteroatom in 1-hetero-3-methyl-3-silacyclohexanes on the structure, stereoelectronic interactions, and relative energies of the conformers is done.}, language = {en} } @article{ZborowskiKochKleinpeteretal.2014, author = {Zborowski, Krzysztof Kazimierz and Koch, Andreas and Kleinpeter, Erich and Proniewicz, Leonard Marian}, title = {Searching for aromatic celate rings. Oxygen versus Thio and Seleno Ligands}, series = {Zeitschrift f{\"u}r physikalische Chemie : international journal of research in physical chemistry and chemical physics}, volume = {228}, journal = {Zeitschrift f{\"u}r physikalische Chemie : international journal of research in physical chemistry and chemical physics}, number = {8}, publisher = {De Gruyter}, address = {Berlin}, issn = {0942-9352}, doi = {10.1515/zpch-2014-0528}, pages = {869 -- 878}, year = {2014}, abstract = {As a part of searching for fully aromatic chelate compounds, copper complexes of malondialdehyde as well as its sulfur and selenium derivatives were investigated using the DFT quantum chemical methods. Chelate complexes of both Cu(I) and Cu(II) ions wereconsidered. Aromaticity of the metal complexes studied were analyzed using NICS(0), NICS(1), PDI, I-ring, MCI, ICMCI and I-B aromaticity indices, and by TSNMRS visualizations of the spatial magnetic properties. It seems that partial aromaticityof studied chelates increases when oxygen atoms in malondialdehyde are replaced by sulfur and selenium.}, language = {en} } @misc{Kleinpeter2014, author = {Kleinpeter, Erich}, title = {Quantification and visualization of the anisotropy effect in NMR spectroscopy by through-space NMR shieldings}, series = {Annual reports on NMR spectroscopy}, volume = {82}, journal = {Annual reports on NMR spectroscopy}, editor = {Webb, GA}, publisher = {Elsevier}, address = {San Diego}, isbn = {978-0-12-800184-4}, issn = {0066-4103}, doi = {10.1016/B978-0-12-800184-4.00003-5}, pages = {115 -- 166}, year = {2014}, abstract = {The anisotropy effect of functional groups (respectively the ring-current effect of aryl moieties) in H-1 NMR spectra has been computed as spatial NICS (through-space NMR chemical shieldings) and visualized by iso-chemical-shielding surfaces of various size and low(high) field direction. Hereby, the anisotropy/ring-current effect, which proves to be the molecular response property of spatial NICS, can be quantified and can be readily employed for assignment purposes in proton NMR spectroscopy-characteristic examples of stereochemistry and position assignments (the latter in supramolecular structures) will be given. In addition, anisotropy/ring-current effects in H-1 NMR spectra can be quantitatively separated from the second dominant structural effect in proton NMR spectra, the steric compression effect, pointing into the reverse direction, and the ring-current effect, by far the strongest anisotropy effect, can be impressively employed to visualize and quantify (anti) aromaticity and to clear up standing physical-organic phenomena as are pseudo-, spherical, captodative, homo-and chelatoaromaticity, to characterize the pi-electronic structure of, for example, fulvenes, fulvalenes, annulenes or fullerenes and to differentiate aromatic and quinonoid structures.}, language = {en} } @article{ShainyanKleinpeter2014, author = {Shainyan, Bagrat A. and Kleinpeter, Erich}, title = {Conformational flexibility of 4,4-dimethyl-3,4-dihydro-2H-1,4-thiasiline and its monoheterocyclic analogs}, series = {Russian journal of general chemistry}, volume = {84}, journal = {Russian journal of general chemistry}, number = {7}, publisher = {Pleiades Publ.}, address = {New York}, issn = {1070-3632}, doi = {10.1134/S1070363214070135}, pages = {1325 -- 1329}, year = {2014}, abstract = {Conformational behavior of the first cyclic organosilicon vinylsulfide, 4,4-dimethyl-3,4-dihydro-2H-1,4-thiasiline as well as its monoheterocyclic analogs, 3,4-dihydro-2H-pyran, 3,4-dihydro-2H-thiopyran, and 1,1-dimethyl-1,2,3,4-tetrahydrosiline is studied in comparison with the carbocyclic analog, cyclohexene, using the methods of low-temperature NMR spectroscopy and theoretical calculations at the DFT and MP2 levels of theory. The barrier to the ring inversion with respect to that in cycloxene is increased in 3,4-dihydro-2H-pyran and 1,1-dimethyl-1,2,3,4-tetrahydrosiline, but, in contrast to the suggestions made in the literature, is decreased in 3,4-dihydro-2H-thiopyran. In 4,4-dimethyl-3,4-dihydro-2H-1,4-thiasiline the barrier is intermediate between those in the corresponding monoheterocycles, 1,1-dimethyl-1,2,3,4-tetrahydrosiline and 3,4-dihydro-2H-thiopyran. The observed variations are rationalized from the viewpoint of the interaction of the pi-electrons of the C=C double bond with the orbitals of heteroatoms in the ring. The structure of the transition state for the ring inversion is discussed.}, language = {en} } @article{ShainyanMoskalikHeydenreichetal.2014, author = {Shainyan, Bagrat A. and Moskalik, Mikhail Yu and Heydenreich, Matthias and Kleinpeter, Erich}, title = {Conformational equilibrium and dynamic behavior of bis-N-triflyl substituted 3,8-diazabicyclo[3.2.1]octane}, series = {Magnetic resonance in chemistry}, volume = {52}, journal = {Magnetic resonance in chemistry}, number = {8}, publisher = {Wiley-Blackwell}, address = {Hoboken}, issn = {0749-1581}, doi = {10.1002/mrc.4086}, pages = {448 -- 452}, year = {2014}, abstract = {Restricted rotation about the N-S partial double bonds in a bis-N-triflyl substituted 3,8-diazabicyclo[3.2.1]octane derivative 1 has been frozen at low temperature (Delta G* = 11.6 kcal mol(-1)), and the existence of all four rotamers about the two N-S bonds, 3-in, 8-in, 3-in, 8-out, 3-out, 8-in, and 3-out, 8-out, respectively, proved experimentally by NMR spectroscopy and theoretically by DFT and MP2 calculations. Copyright (C) 2014 John Wiley \& Sons, Ltd.}, language = {en} } @article{KleinpeterKlaumuenzer2014, author = {Kleinpeter, Erich and Klaumuenzer, Ute}, title = {Quantification of the push-pull Effect in disubstituted alkynes - Application of occupation quotients pi*/pi and C-13 chemical shift differences Delta delta(C C)}, series = {Journal of molecular structure}, volume = {1074}, journal = {Journal of molecular structure}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0022-2860}, doi = {10.1016/j.molstruc.2014.05.072}, pages = {193 -- 195}, year = {2014}, abstract = {Structures, C-13 chemical shifts, and the occupation quotients of anti-bonding pi* and bonding pi orbitals of the C C triple bond along a series of push-pull alkynes (p)X-C6H4 C(O)-C C-NH-C6H4-Y(P) (X,Y= H, Me, OMe, NMe2, NO2, COMe, COOMe, F, Cl, Br) were computed at the DFT level (B3LYP/6-311G**) of theory. Both the stereochemistry (cis/trans-isomers) by steric twist and the push-pull character by both C-13 chemical shift differences (Delta delta(C C)) and the occupation quotient (pi(C C)/pi(C C)) were studied; the latter two parameters can be readily employed to precisely quantify the push-pull effect in alkynes. (C) 2014 Elsevier B.V. All rights reserved.}, language = {en} } @article{KleinpeterKochSchulzetal.2014, author = {Kleinpeter, Erich and Koch, Andreas and Schulz, Stefanie and Wacker, Philipp}, title = {Interplay of para- and diatropic ring currents [(anti)aromaticity] of macrocyclic rings subject to conformational influences, further annelation and hydrogenation of aromatic ring moieties}, series = {Tetrahedron}, volume = {70}, journal = {Tetrahedron}, number = {48}, publisher = {Elsevier}, address = {Oxford}, issn = {0040-4020}, doi = {10.1016/j.tet.2014.10.018}, pages = {9230 -- 9239}, year = {2014}, abstract = {The spatial magnetic properties (Through Space NMR Shieldings-TSNMRS) of a variety of porphyrins, hemiporphyrazines and tetraoxo[8]circulenes have been computed, visualized as Iso-chemical Shielding Surfaces (ICSS) of various size and direction, and were examined subject to the interplay of present (para)-diatropic ring currents [(anti)aromaticity] and influences on the latter property originating from the macrocyclic ring conformation, further annelation and partial to complete hydrogenation of aromatic ring moieties. Caution seems to be indicated when concluding from a single NICS parameter to present (para)diatropic ring currents [(anti)aromaticity]. (C) 2014 Elsevier Ltd. All rights reserved.}, language = {en} } @article{KleinpeterKoch2011, author = {Kleinpeter, Erich and Koch, Andreas}, title = {Chelatoaromaticity-existing: yes or no? An answer given by spatial magnetic properties (through space NMR shieldings-TSNMRS)}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {13}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, number = {46}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c1cp21942a}, pages = {20593 -- 20601}, year = {2011}, abstract = {The spatial magnetic properties (through space NMR shieldings-TSNMRS) of metal complexes (with ligands such as acetylacetone, 3-hydroxy-pyran(4) one) and "metallobenzenes" have been calculated by the GIAO perturbation method and visualized as Iso-Chemical-Shielding Surfaces (ICSS) of various sizes and directions. The TSNMRS values, thus obtained, can be successfully employed to quantify and visualize partial aromaticity of the metallocyclic ring by comparison with the spatial magnetic properties of the corresponding non-complexed ligands in comparable structural and electronic situations, and benzene, respectively. Because anisotropy/ring current effects in H-1 NMR spectra proved to be the molecular response property of TSNMRS, the results obtained concerning partial "chelatoaromaticity" are experimentally ensured.}, language = {en} } @article{KleinpeterLaemmermannKuehn2011, author = {Kleinpeter, Erich and Laemmermann, Anica and K{\"u}hn, Heiner}, title = {The anisotropic effect of functional groups in H-1 NMR spectra is the molecular response property of spatial nucleus independent chemical shifts (NICS)-Conformational equilibria of exo/endo tetrahydrodicyclopentadiene derivatives}, series = {Organic \& biomolecular chemistry : an international journal of synthetic, physical and biomolecular organic chemistry}, volume = {9}, journal = {Organic \& biomolecular chemistry : an international journal of synthetic, physical and biomolecular organic chemistry}, number = {4}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1477-0520}, doi = {10.1039/c0ob00356e}, pages = {1098 -- 1111}, year = {2011}, abstract = {The inversion of the flexible five-membered ring in tetrahydrodicyclopentadiene (TH-DCPD) derivatives remains fast on the NMR timescale even at 103 K. Since the intramolecular exchange process could not be sufficiently slowed for spectroscopic evaluation, the conformational equilibrium is thus inaccessible by dynamic NMR. Fortunately, the spatial magnetic properties of the aryl and carbonyl groups attached to the DCPD skeleton can be employed in order to evaluate the conformational state of the system. In this context, the anisotropic effects of the functional groups in the H-1 NMR spectra prove to be the molecular response property of spatial nucleus independent chemical shifts (NICS).}, language = {en} }