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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

Research paper by Bagrat A. Shainyan, Svetlana V. Kirpichenko, Nina N. Chipanina, Larisa P. Oznobikhina, Erich Kleinpeter, Sergey A. Shlykov, Dmitriy Yu. Osadchiy

Indexed on: 10 Dec '15Published on: 20 Nov '15Published in: Journal of Organic Chemistry



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 1H and 13C 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 (−ΔG°103 = 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-silatetrahydropyran 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.

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