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

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

“…Note, that the CeC(S) bond is about 0.01 Å shorter than the CeC(Si) bond, as follows both from the experiment and calculations. The same is true for other silaheterocyclohexanes irrespective of the nature of heteroatom in the ring e nitrogen [8,18] or oxygen [19].…”

“…This value is close to those in 1-methyl-1-silacyclohexane, being 46.0(31) as determined from GED [5] for the two conformers, and 43.1(3) for the equatorial and 42.8(3) for the axial conformer as measured by microwave spectroscopy [21]. The Flap(S) ¼ 52.3 is larger than the Flap(C) in cyclohexane, but smaller than the Flap(O) in 3-methyl-3-phenyl-3-silatetrahydropyran, which amounts to 65 [19].…”

Stereochemistry of 3-isopropoxy-3-methyl-1,3-oxasilinane–the first 3-silatetrahydropyran with an exo-cyclic RO–Si bond

“…This result is very close to values for related heterocycles: 1-methyl-1-phenyl-1-silacyclohexane (0.12 kcal/mol), 3-methyl-3-phenyl-3-silathiane (0.15 kcal/mol), 39 1,3-dimethyl-3-phenyl-3-silapiperidine (0.24 kcal/mol), 40 1-isopropyl-3-methyl-3-phenyl-3-silapiperidine (0.3 kcal/mol) 41 and 3-methyl-3-phenyl-3-silatetrahydropyran (0.16 kcal/mol). 44 However, while in the former analogues the conformer with the methyl substituent in axial position proves to be clearly preferred the present conformational equilibrium proves equalized amounts of the conformers. The reason therefore seems to be the more polar nature of the Si−i-OPr substituent compared with methyl.…”

“…The Gibbs free energy of activation ∆G # proves to be 4.5 kcal/mol, in good agreement with theoretical calculations (vide infra). This is considerably lower than in tetrahydropyran (10.3 kcal/mol, CH 3 OD/CHClF 2 ) 46 due to the aforementioned specific structural features of silacyclohexanes, and even a little lower than in 3-methyl-3-phenyl-3-silatetrahydropyran (4.7 kcal/mol), 44 apparently due to less crowded arrangement of substituents (Me,OR vs. Me,Ph) at the silicon atom.…”

At the Experimental Limit of the NMR Conformational Analysis: 29Si and 13C NMR Study of the Conformational Equilibrium of 1-Phenyl-1-tert-butylsilacyclohexane

“…In continuation of our ongoing research on the conformational analysis of silacyclohexanes and sila­(hetero)­cyclohexanes summarized in the recent review, we synthesized 1-phenyl-1- tert- butyl-silacyclohexane ( 1 ) and examined its molecular structure and conformational preferences by gas-phase electron diffraction (GED), temperature variable IR spectroscopy and quantum chemistry . Low temperature 1 H and 13 C NMR spectroscopy, usually the most informative method for the analysis of the conformational equilibrium in solution and comparison of the results to those obtained by GED, as we did in many previous works, ,− failed because a trial to freeze the equilibrium led to complete solute precipitation at already 124 K …”