Molecular structure and conformations of 1-phenyl-1-silacyclohexane from gas-phase electron diffraction and quantum chemical calculations

Molecular structure and conformational analysis of 3-methyl-3-phenyl-3-silatetrahydropyran. Gas-phase electron diffraction, low temperature NMR and quantum chemical calculations

“…Barriers of the same order were found for the recently studied analogous molecule of 1-phenyl-1-silacyclohexane, 16 for which they were calculated to be 0.3 to 0.7 kcal/mol for the equatorial conformer and 0.2 to 1.1 kcal/mol for the axial conformer, depending on the method applied. These barriers are slightly higher than those in acyclic phenylsilanes for which nearly free rotation about the Me 3 Si-C Ph 21 or H 3 Si-C Ar bonds 22,23 was found by GED and theoretical calculations.…”

“…The calculations of 1-phenyl-1-silacyclohexane predicted the existence of four conformers with different angles of rotation of the phenyl group -two structures with equatorial and two with axial positions of the phenyl ring. 16 In the present study, only two conformers are observed for 3-methyl-3-phenyl-3-silatetrahydropyran 1 (Fig. 2).…”

“…Obviously, the methyl group bound to the silicon atom, being more bulky than the hydrogen atom, stabilizes the preferred conformers of the compound. 16 For the 1-Ph ax conformer, a shoulder is observed in the PESs (Fig. 1) at the dihedral angle C8-C7-Si-C13 of ca.…”

Molecular structure and conformational analysis of 3-methyl-3-silathiane by gas phase electron diffraction, FTIR spectroscopy and quantum chemical calculations

“…An exception is 1-silyl-1-silacyclohexane [4] for which the SiH 3 -axial conformer predominates in gas phase (GED), whereas in solution at low temperature (NMR) the ratio of the conformers is reversed. For X ¼ Me [5] or Ph [6,7], the equatorial conformers predominate with the ax/eq ratio of ca. 1:2 in gas phase at room temperature (GED) and ca.…”

Structure and conformational behavior of N-phenylpiperidine studied by gas-phase electron diffraction and quantum chemical calculations

“…At the same time, for the bulkier heteroatoms in the cyclohexane ring, Si or P, the theoretical predictions are principally contradictive. The equatorial conformer is, in terms of DE, 1.07 [30] and 0.48 kcal/mol more stable than the axial when calculated with DFT-B3LYP, but opposite tendencies were observed in the MP2 calculations, e0.38 [30] and À0.90 kcal/mol, for silicon and phosphorus heteroatoms, respectively. The B3LYP-GD3/6-311G** calculations predict the DE values to be À0.09 and À1.13 kcal/mol for PhSiC and PhPhr, respectively, while, from the Gibbs energies, the equatorial (PhSiC) and the axial (PhPhr) conformers are preferable.…”