Refine
Year of publication
Document Type
- Article (299)
- Monograph/Edited Volume (3)
- Other (3)
- Conference Proceeding (1)
- Part of Periodical (1)
- Postprint (1)
- Review (1)
Is part of the Bibliography
- yes (309) (remove)
Keywords
- Conformational analysis (14)
- NMR spectroscopy (9)
- conformational analysis (9)
- NICS (8)
- Theoretical calculations (8)
- Through-space NMR shieldings (TSNMRS) (8)
- Anisotropy effect (7)
- Ring current effect (7)
- Aromaticity (6)
- NMR (6)
- DFT calculations (5)
- Dynamic NMR (5)
- Quantum chemical calculations (5)
- quantum chemical calculations (5)
- ICSS (4)
- TSNMRS (4)
- Conformational equilibrium (3)
- GIAO (3)
- Gas phase electron diffraction (3)
- NBO analysis (3)
- dynamic NMR (3)
- (Anti)aromaticity (2)
- Anisotropic effect (2)
- Barrier to ring inversion (2)
- Chelatoaromaticity (2)
- DFT (2)
- Density functional calculations (2)
- Dynamic NMR spectroscopy (2)
- H-1 NMR (2)
- Iso-chemical-shielding surfaces (ICSS) (2)
- NHCs (2)
- Push-pull character (2)
- Push-pull effect (2)
- Stereochemistry (2)
- Steric effect (2)
- Taft equation (2)
- anisotropic effects (2)
- aromaticity (2)
- low-temperature NMR spectroscopy (2)
- modified Mannich reaction (2)
- shieldings (TSNMRS) (2)
- (1)H NMR (1)
- (13)C NMR (1)
- (TSNMRS) (1)
- 1,1-dimethyl-1,2,3,4-tetrahydrosiline (1)
- 1,2,4-Dithiazole (1)
- 1,2-Dithiole (1)
- 1,2-diboretane-3-ylidene (1)
- 1,3-Azasilinanes (1)
- 1,3-Dimethyl-3-phenyl-1,3-azasilinane (1)
- 1,3-Oxasilinanes (1)
- 1,4,2-Oxazasilinanes (1)
- 1-(Dimethylamino)-1-phenyl-1-silacyclohexane (1)
- 1-Methylthio-1-phenyl-1-silacyclohexane (1)
- 2 (1)
- 2,2-Disubstituted adamantane derivatives (1)
- 2-Alkylidene-4-oxothiazolidine (1)
- 2-Substituted adamantane derivatives (1)
- 3,4-Dihydroisoquinoline (1)
- 3,4-dihydro-2H-pyran (1)
- 3,4-dihydro-2H-thiopyran (1)
- 3-Fluoro-3-methyl-3-silatetrahydropyran (1)
- 3-Silatetrahydropyrans (1)
- 3-silathianes (1)
- 3c,2e-bonding (1)
- 4,4-dimethyl-3,4-dihydro-2H-1,4-thiasiline (1)
- 4-Oxothiazolidine (1)
- 4-Substituted cyclohexanones (1)
- 4-methylene-cyclohexyl pivalate (1)
- 4-silapiperidines (1)
- 4-silathianes (1)
- 6-disilamorpholines (1)
- 9-Arylfluorenes (1)
- A-values of COOAr on cyclohexane (1)
- ALTONA equation (1)
- ATR-FTIR (1)
- Ab initio MO computations (1)
- Additivity of conformational energies (1)
- Aminonaphthol (1)
- Aminonaphthols (1)
- Annelation effect (1)
- Anserine (1)
- Anti-aromaticity (1)
- Anticancer (1)
- Antileishmanial (1)
- Antiplasmodial (1)
- Aromatic or quinonoid (1)
- Assignment of stereochemistry (1)
- Asteraceae (1)
- B,N heterocycles (1)
- B3LYP/6-31+G(d,p) calculations (1)
- B3LYP/6-311++G** (1)
- Barrier to rotation about C-N bond (1)
- Benzazepine (1)
- Benzenoid structure (1)
- Benzenoid structures (1)
- Benzoic acid esters (1)
- Benzyne-allene or cumulene-like structure (1)
- Betaines (1)
- Binding pocket position (1)
- C-13 (1)
- C-13 NMR (1)
- C-13 NMR spectroscopy (1)
- C-13 chemical shift (1)
- C-13 chemical shift difference Delta delta(C C) (1)
- CAACs (1)
- CH center dot center dot center dot O hydrogen bonds (1)
- Carbamoyl tetrazoles (1)
- Carbene or zwitterions (1)
- Carbenes (1)
- Carbohydrates (1)
- Carvotacetones (1)
- Chiral dopants (1)
- Condensed thiazolidines (1)
- Conformation analysis (1)
- Conformational equilibria (1)
- Copper Metal Complexes (1)
- Cyanine/merocyanine-like structures (1)
- Cyclazines (1)
- Cyclobutylcarbene (1)
- Cyclohexyl esters (1)
- DFT and MP2 calculations (1)
- DFT and MP2 simulation (1)
- DFT calculation (1)
- DFT structural study (1)
- DFT theoretical calculations (1)
- Dative vs. coordinative NHC -> BR3 bond (1)
- Dehydro[n]annulenes (1)
- Diastereomers assignment (1)
- Diastereoselectivity (1)
- Dual Scale Factors (1)
- Dual scale factors (1)
- Dynamic H-1-NMR (1)
- Electrostatic effects (1)
- F-19 (1)
- GIAO calculations (1)
- Gas-phase electron diffraction (1)
- Glycol podands (1)
- H-1 (1)
- H-1 NMR spectroscopy (1)
- Hammett-Brown plots (1)
- Hemiporphyrazines (1)
- Heterocycles (1)
- IR and Raman spectra (1)
- Iso-chemical shielding surfaces (ICSS) (1)
- Isothiocyanic acid (1)
- Low temperature NMR spectroscopy (1)
- Low-temperature C-13 and Si-29 NMR (1)
- Low-temperature NMR (1)
- Low-temperature d-NMR (1)
- M062X/6-311G** calculations (1)
- MP2 (1)
- MP2 and CCSD(T) calculations (1)
- Matrix IR spectrum (1)
- Mesomeric equilibrium of carbene/zwitterion (1)
- Mesomerism (1)
- Modified Mannich reaction (1)
- Molecular dynamics (1)
- Multiple NHC(CAAC)-Boron bonds (1)
- N-acetyl glucosamine derivatives (1)
- N-unsubstituted (primary)S-thiocarbamates (1)
- N-unsubstituted(primary)O-thiocarbamates (1)
- NBO and STERIC analyses (1)
- NBO/NCS analysis (1)
- Naphthoxazines (1)
- Naphthoxazinoquinazolines (1)
- Naphthoxazinoquinazolinones (1)
- Occupation quotient pi*/pi (1)
- Peripheral ring current (1)
- Polar effect (1)
- Polar substituent constant (1)
- Porphyrins (1)
- Push-pull alkynes (1)
- Push-pull allenes (1)
- Quantum Chemical Calculations (1)
- Quasi-aromaticity (1)
- Quinazolines (1)
- Quinonoid structure (1)
- Quotient method (1)
- RA-intramolecular hydrogen bond (1)
- Rearrangement to trithiaazapentalene (1)
- Residual dipolar couplings (1)
- Ring-current effect (1)
- SQM FF (1)
- SQM-FF (1)
- Salicylic acid (1)
- Silacyclohexanes (1)
- Silaheterocyclohexanes (1)
- Silica sulfuric acid (1)
- Simulation of H-1 NMR spectra (1)
- Solid acid (1)
- Solvent effects (1)
- Solvent-free (1)
- Spatial NICS (1)
- Sphaeranthus bullatus (1)
- Steric effects (1)
- Steric hindrance (1)
- Steric substituent constant (1)
- Substituent chemical shifts (1)
- Substituent effects (1)
- Sulfoxide (1)
- Supramolecular compounds (1)
- Tautomerism (1)
- Tetraoxo[8]circulenes (1)
- Thienopyridine (1)
- Through -space NMR (1)
- Through-space NMR (1)
- Through-space NMR shielding (TSNMRS) (1)
- Trithiapentalene (1)
- Trough-space NMR shieldings (TSNMRS) (1)
- Twisted double bonds (1)
- Vinylogous N-acyliminium ion (1)
- X-ray analysis (1)
- Y-aromaticity (1)
- Ylide (1)
- [4+2] cycloaddition (1)
- ab initio calculations (1)
- barrier to ring inversion (1)
- benzenoid structures (1)
- carbene electron deficiency (1)
- carbenes (1)
- cis,cis-Tricyclo[5.3.0.0(2,6)]dec-3-enes (1)
- computational chemistry (1)
- conformational equilibrium (1)
- cyclic imines (1)
- cycloaddition (1)
- density functional calculations (1)
- dielectric spectroscopy (1)
- dynamic NMR spectroscopy (1)
- endo-Mode cyclization (1)
- ephedrine/pseudoephedrine (1)
- exo-methylene conformational effect at cyclohexane (1)
- low temperature NMR spectroscopy (1)
- molecular structure (1)
- nucleus-independent chemical shift (1)
- nucleus-independent chemical shifts (NICS) (1)
- onformational analysis (1)
- ortho-quinone methide (o-QMs) (1)
- para-Nitro-pyridine N-oxides (1)
- pi interactions (1)
- pi-Electron delocalization (1)
- pi-Stacking (1)
- quinoid structures (1)
- restricted N-S rotation (1)
- silacyclohexanes (1)
- silapiperidines (1)
- siloxanes (1)
- spectroscopy (1)
- sulfimides (1)
- sulfur heterocycles (1)
- through space NMR shieldings (1)
- zwitterions (1)
The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of benzenoid and quinoid tautomeric structures such as benzodifurantrione and phenazine-type molecules have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept of Paul von Rague Schleyer and visualized as iso- chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values were employed to quantify and visualize the partial aromaticity of the studied compounds. In the case of the surprisingly more stable quinoid tautomers, the aromaticity-synonymous with stability due to the conjugation of p electrons and lone pairs-was not found to be particularly reduced.
The spatial magnetic properties, through-space NMR shieldings (TSNMRS), of benzenoid and quinoid tautomeric structures such as benzodifurantrione and phenazine-type molecules have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept of Paul von Rague Schleyer and visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The TSNMRS values were employed to quantify and visualize the partial aromaticity of the studied compounds. In the case of the surprisingly more stable quinoid tautomers, the aromaticity-synonymous with stability due to the conjugation of p electrons and lone pairs-was not found to be particularly reduced.
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.
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.
Geometry, 11B, 13C chemical shifts and the spatial magnetic properties (Through-Space NMR Shieldings -TSNMRS) of both cations and anions of boron-trapped N-heterocyclic carbenes (NHCs) and cyclic (alkyl)(amino)carbenes (CAACs) and of the corresponding diborane/diborene/diboryne dis-carbene adducts have been calculated using the GIAO perturbation method employing the nucleus independent chemical shift (NICS) concept; the TSNMRS results are visualized as iso-chemical-shielding surfaces (ICSS) of various size and direction. The ICSS of the TSNMRS (actually the anisotropy effects measurable in 1H NMR spectroscopy) are employed to qualify and quantify the present multiple bond character of the Carbene-Boron bond in the trapped NHCs and CAACs. Results are confirmed by bond length and 11B/13C chemical shift variations. Thus the partial multiple bond character of the Carbene-Boron bond cannot be expressed by the arrow of weak, much longer dative bonds and should be omitted as in other covalent lone pair-it or triel bonds. & COPY; 2023 Elsevier Ltd. All rights reserved.
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.
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.
13C chemical shifts of the push;pull oligoalkynes Don-(C;C)n-Acc (n = 1;4; Don = morpholino; Acc = COMe, COOMe) were computed at the DFT (B3LYP/6-311+G(d,p) level of theory compared with the experimental ; values and the agreement employed as a measure of quality for the underlying structures. For the global minima structures, the occupation quotients of antibonding ;* and bonding ; orbitals (;*C;C/ ;C;C) and the bond lengths (dC;C) of the various C;C triple bonds were also computed and correlated to each other. The linear dependence obtained for the two parameters dC;C and ;*C;C/ ;C;C quantifies changes in ;-delocalization induced by the push;pull effect of the substituents and 1,3-conjugation (1,3,5- and 1,3,5,7-, respectively) of the C;C bonds in the oligoalkynes studied. A critical comparison of the push;pull effect, attenuated with increasing n, and the conjugative stabilization of the oligoalkynes, increasing with n, as concluded from dC;C and ;*C;C/;C;C of the oligoalkynes and the reference compounds Me-(C;C)n-Me, Don-(C;C)n-Me, and Me-(C;C)n-Acc), respectively (Don = morpholino; Acc = COMe, COOMe), is affiliated.
The through space NMR shielding (TSNMRS) values of two tricyclobutabenzene (TCBB) derivatives 2, of the corresponding hexamethylene and hexaoxo TCBB derivatives 3, of [4n]annuleno[4n + 2]annulene 5 and of its tricyclobutadiene parent compound 4 have been ab initio calculated by the GIAO perturbation method employing the nucleus- independent chemical shift (NICS) concept of Paul von Ragué Schleyer, and visualized as iso-chemical shielding surfaces (ICSS). TSNMRS values can be successfully employed to quantify and visualize the aromaticity of the central, and in 5 also of the terminal benzene ring moieties.
Prototypes for homoaromaticity in cations, neutral molecules, and anions are theoretically studied at the MP2 level of theory. For the global minimum structures on the potential energy surface both 1H/13C chemical shifts and spatial magnetic properties as through space NMR shieldings (TSNMRS) were calculated by the GIAO perturbation method. The TSNMRS are visualized as iso-chemical-shielding surfaces (ICSS) of different sign and size. Coincident experimental and computed 1H/13C chemical shifts afforded the possibility to decide from the TSNMRSs at hand on both the existence and the size of homoaromaticity in the molecules studied.
The through space NMR shieldings (TSNMRS) of dodecahedrane C20H20, of the isomeric hydrocarbons C20H12, of the ions C20H122+ and C20H122- of the fluxional fullerene C20 and of its dication C202+ have been ab initio calculated employing the NICS concept on basis of MP2/6-31G* geometries and visualized as iso-chemical-shielding/deshielding surfaces (ICSSs). TSNMRS values were employed to study the exohedral magnetic properties of the compounds studied. Hereby, the curved It-conjugation in the compounds studied could be quantified.
Identification of benzenoid and quinonoid structures by through-space NMR shieldings (TSNMRS)
(2010)
Rotation about the single bond adjoining the aryl and fluorene moieties in 9-arylfluorenes can be frozen out on the NMR timescale if methyl groups are located at either one or both of the ortho positions of the aryl substituent. In the ground-state of these rotamers, the planes of the aryl and fluorene moieties are perpendicular to each other and the methyl protons are either shielded or deshielded, respectively, due to the ringe current effect of the fluorene moiety. This anisotropic effect on the 1H chemical shifts of the methyl protons has been quantified on the basis of through- space NMR shieldings (TSNMRS) and subsequently _______ compared with the experimentally observed chemical shift differences _____. In this context, the experimental anisotropic effects of functional groups in the !H NMR have proven to quantitatively be the molecular response property of theoretical spatial nucleus independent chemical shieldings (NICS). Differences between _______ and _____ were, for the first time, also quantified as arising from steric compression.
The spatial magnetic properties (Through-Space NMR Shieldings-TSNMRS) of already synthesized dehydro[n]annulenes of various ring size (from C-12 to C-20) have been computed, visualized as Isochemical Shielding Surfaces (ICSS) of various size and direction, and were examined subject to present (anti)aromaticity. For this purpose the thus quantified ring current effect of the macro cycles on proximate protons in proton NMR spectra was employed.
The spatial magnetic properties (through-space NMR shieldings, or TSNMRSs) of the antiaromatic 9-oxaanthracene anion 12(-) and of the corresponding 9-dimeric dianion 11(2-) have been calculated by the gauge-invariant atomic orbitals (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 indicate antiaromaticity by paratropic ring currents of the anionic compounds of 11(2-) and 12(-) studied and other neutral and ionic antiaromatic molecules from previous studies because anisotropic effects of functional groups in H-1 NMR spectra have quantitatively proven to be the molecular response property of theoretical spatial nucleus independent chemical shieldings (NICS).
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.
Characterization and quantification of quasi-aromaticity by spatial magnetic properties (TSNMRS)
(2015)
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.
Rotation about the single bond adjoining the aryl and fluorene moieties in 9-arylfluorenes can be frozen out on the NMR timescale if methyl groups are located at either one or both of the ortho positions of the aryl substituent. In the ground-state of these rotamers, the planes of the aryl and fluorene moieties are perpendicular to each other and the methyl substituents are consequently positioned either above the fluorene moiety or in-plane with it; thus, the methyl protons are either shielded or deshielded, respectively, due to the ring current effect of the fluorene moiety. This anisotropic effect on the H-1 chemical shifts of the methyl protons has been quantified on the basis of through-space NMR shieldings (TSNMRS) and subsequently Delta delta(calcd) compared with the experimentally observed chemical shift differences, Delta delta(exp). In this context, the experimental anisotropic effects of functional groups in the H-1 NMR have proven to quantitatively be the molecular response property of theoretical spatial nucleus independent chemical shieldings (NICS). Differences between Delta delta(calcd) and Delta delta(exp) were, for the first time, also quantified as arising from steric compression.