TY - JOUR A1 - Shainyan, Bagrat A. A1 - Ushakov, Igor A. A1 - Meshcheryakov, Vladimir I. A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - Variable temperature NMR and theoretical study of the stereodynamics of 5-trifluoromethylsulfonyl-1,3,5- dioxaazinane : Perlin effect subject to heteroatom substitution N2 - Multinuclear dynamic NMR spectroscopy of 5-trifluoromethylsulfonyl-1,3,5-dioxaazinane (4) revealed the existence of two close in energy chair conformers with differently oriented CF3 groups with respect to the ring. Of the two alternative routes for their interconversion, the ring inversion path with intermediate formation of the corresponding 2,5-twist-conformer is preferred, with the energy barrier of 11.2 kcal/mol in excellent agreement with the experimental value (11.7 kcal/mol). The Perlin effect is studied experimentally and calculated theoretically for all CH2 groups and found to be subject to the nature of the adjacent heteroatoms O and N, respectively. Y1 - 2008 ER - TY - JOUR A1 - Shainyan, Bagrat A. A1 - Ushakov, Igor A. A1 - Meshcheryakov, Vladimir I. A1 - Schilde, Uwe A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - The stereodynamics of 3,5-bis(trifluoromethylsulfonyl)-1,3,5-oxadiazinane and 1,3,5- tris(trifluoromethylsulfonyl)-1,3,5-triazinane- an experimental and theoretical study N2 - Multinuclear dynamic NMR spectroscopy of 3,5-bis(trifluoromethylsulfonyl)-1,3,5-oxadiazinane (3) revealed the existence of two conformers with differently oriented CF3 groups with respect to the ring, and two dynamic processes: ring inversion and restricted rotation about the N-S bond. Two transition states connecting the two conformers and corresponding to clockwise and counterclockwise rotations about the N-S bond were found; the calculated activation barriers of about 12 kcal/mol are in excellent agreement with those measured experimentally for the related molecule 1,3,5-tris(trifluoromethylsulfonyl)-1,3,5-triazinane (1). X-ray analysis proved the existence of the symmetric isomer of 3, which is the minor isomer in solutions but the only one in the crystal due to packing effects. The normal Perlin effect (JCHax < JCHeq)observed for 2(6)-CH2 in 3, whereas the reversed Perlin effect was found for the 4-CH2 group in 3 as well as for all CH2 groups in 1 both experimentally and theoretically. The latter effect in compounds 1, 3, and 1- (methylsulfonyl)-3,5-bis(trifluoromethylsulfonyl)-1,3,5-triazinane (2) can be considered as a genuine reverse Perlin effect since larger values of 1JCH are observed for longer C-H bonds. Y1 - 2007 UR - http://www.sciencedirect.com/science/article/pii/S0040402007016389 U6 - https://doi.org/10.1016/j.tet.2007.09.041 ER - TY - JOUR A1 - Shainyan, Bagrat A. A1 - Ushakov, Igor A. A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - Stereodynamics of 1-(methylsulfonyl)-3,5-bis(trifluoromethylsulfonyl)-1,3,5-triazinane: Experimental and theoretical analysis N2 - Dynamic NMR of 1-(methylsulfonyl)-3,5-bis(trifluoromethylsulfonyl)-1,3,5-triazinane reveals the existence of three conformers and two dynamic processes: ring inversion and rotation about the N-S bond, both processes having Delta G(double dagger) = 13.5 kcal/mol. An unprecedented large reverse Perlin effect (J(CHax) > J(CHeq)) was found experimentally and calculated theoretically. Y1 - 2006 UR - http://pubs.acs.org/doi/full/10.1021/jo061112x U6 - https://doi.org/10.1021/Jo061112x ER - TY - JOUR A1 - Meshcheryakov, Vladimir I. A1 - Moskalik, Mikail Yu. A1 - Kelling, Alexandra A1 - Schilde, Uwe A1 - Ushakov, Igor A. A1 - Shainyan, Bagrat A. T1 - Oxymethylation of trifluoromethanesulfonamide with paraformaldehyde in ethyl acetate N2 - Acid-catalyzed reaction of trifluoromethanesulfonamide with paraformaldehyde in ethyl acetate led to the formation of oxymethylated products that did not form in the reaction carried out in sulfuric acid. Following products were obtained: 5-trifluoromethylsulfonyl-1,3-dioxazinane, 3,7-bis-(trifluoromethylsulfonyl)-1,5,3,7-dioxadiazocane, and a complex of trifluoromethanesulfonamide with 2,4,8,10-tetraoxospiro[5,5]undecene, 1:1. The spiroring resulted from the cyclization of pentaerythritol under the action of formaldehyde. The pentaerythritol formed in its turn by oxymethylation of the methyl group of ethyl acetate with paraformaldehyde followed by the reduction of the COOEt group into CH2 OH by the formaldehyde. Y1 - 2008 UR - http://springer.metapress.com/content/q58m84577ng74p3g/ ?p=0be1219998b44c288f855f33f6168bf6&pi=19 U6 - https://doi.org/10.1134/S1070428008020206 SN - 1070-4280 ER - TY - JOUR A1 - Shainyan, Bagrat A. A1 - Ushakov, Igor A. A1 - Tolstikova, Ljudmila L. A1 - Koch, Andreas A1 - Kleinpeter, Erich T1 - N-Trifyl substituted 1,4-diheterocyclohexanesùstereodynamics and the Perlin effect N2 - The stereodynamic behaviour of 1-(trifluoromethylsulfonyl)piperidine 1, 4-(trifluoromethylsulfonyl)morpholine 2, 1,4-bis(trifluoromethylsulfonyl)piperazine 3 and 4-(trifluoromethylsulfonyl)thiomorpholine 1,1-dioxide 4 was studied by low-temperature 1H, 13C and 19F NMR spectroscopies. In acetone solution, compounds 1, 2 and 4 were found to exist as mixtures of two conformers in the ratio of 4:1, 4:1 and 8:1, respectively, differing by orientation of the CF3 group with respect to the ring. Compound 3 exists as a mixture of three conformers in the ratio of 3:28:69 also differing by the orientation of the two CF3 groups. Unlike the previously studied N-trifyl substituted 1,3,5-triheterocyclohexanes, the preferred conformers of compound 1 and of 1,4-diheterocyclohexanes 2-4 are those with the CF3 group directed outward from the ring, which is caused by intramolecular interactions of the oxygen atoms of the CF3SO2N groups with the equatorial hydrogens in the ;-position. B3LYP/6-311+G(d,p) calculations of the energy, geometry and NMR parameters corroborate the experimental data. The calculated Perlin effects for all conformers of compounds 1-4 as well as those measured for the major conformers of compounds 3 and 4 were analyzed by the use of the NBO analysis. Y1 - 2008 ER - TY - JOUR A1 - Kleinpeter, Erich A1 - Kirpichenko, Svetlana V. A1 - Ushakov, Igor A. A1 - Shainyan, Bagrat A. T1 - Conformational analysis of 3-methyl-3-silathiane and 3-fluoro-3-methyl-3-silathiane N2 - The conformational equilibria of 3-methyl-3-silathiane 5, 3-fluoro-3-methyl-3-silathiane 6 and 1-fluoro-1- methyl-1-silacyclohexane 7 have been studied using low temperature 13C NMR spectroscopy and theoretical calculations. The conformer ratio at 103;K was measured to be about 5ax:5eq;=;15:85, 6ax:6eq;=;50:50 and 7ax:7eq;=;25:75. The equatorial preference of the methyl group in 5 (0.35;kcal;mol;1) is much less than in 3-methylthiane 9 (1.40;kcal;mol;1) but somewhat greater than in 1-methyl-1- silacyclohexane 1 (0.23;kcal;mol;1). Compounds 5-7 have low barriers to ring inversion: 5.65 (ax;;;eq) and 6.0 (eq;;;ax) kcal mol;1 (5), 4.6 (6), 5.1 (Meax;;;Meeq) and 5.4 (Meeq;;;Meax) kcal;mol;1 (7). Steric effects cannot explain the observed conformational preferences, like equal population of the two conformers of 6, or different conformer ratio for 5 and 7. Actually, by employing the NBO analysis, in particular, considering the second order perturbation energies, vicinal stereoelectronic interactions between the Si-X and adjacent C-H, C-S, and C-C bonds proved responsible. Y1 - 2011 SN - 0894-3230 ER - TY - JOUR A1 - Kirpichenko, Svetlana V. A1 - Kleinpeter, Erich A1 - Ushakov, Igor A. A1 - Shainyan, Bagrat A. T1 - Conformational Analysis of 3-Methyl-3-Silathiane and 3-Fluoro-3-Methyl-3-Silathiane JF - Journal of physical organic chemistry N2 - The conformational equilibria of 3-methyl-3-silathiane 5, 3-fluoro-3-methyl-3-silathiane 6 and 1-fluoro-1-methyl-1- silacyclohexane 7 have been studied using low temperature C-13 NMR spectroscopy and theoretical calculations. The conformer ratio at 103 K was measured to be about 5(ax):5(eq) - 15:85, 6(ax):6(eq)-50:50 and 7(ax):7(eq)-25:75. The equatorial preference of the methyl group in 5 (0.35 kcal mol(-1)) is much less than in 3-methylthiane 9 (1.40 kcal mol(-1)) but somewhat greater than in 1-methyl-1-silacyclohexane 1 (0.23 kcal mol(-1)). Compounds 5-7 have low barriers to ring inversion: 5.65 (ax -> eq) and 6.0 kcal mol(-1) (eq -> ax) (5), 4.6 kcal mol(-1) (6), 5.1 kcal mol(-1) (Me-ax -> Me-eq), and 5.4 kcal mol(-1) (Me-eq -> Me-ax) (7). Steric effects cannot explain the observed conformational preferences, like equal population of the two conformers of 6, or different conformer ratio for 5 and 7. Actually, by employing the NBO analysis, in particular, considering the second order perturbation energies, vicinal stereoelectronic interactions between the Si-X and adjacent C-H, C-S, and C-C bonds proved responsible. KW - conformational analysis KW - low-temperature NMR spectroscopy KW - NBO analysis KW - quantum chemical calculations KW - 3-silathianes Y1 - 2011 U6 - https://doi.org/10.1002/poc.1758 SN - 0894-3230 VL - 24 IS - 4 SP - 320 EP - 326 PB - Wiley-Blackwell CY - Hoboken ER -