Conformational analysis of 3‐methyl‐3‐silathiane and 3‐fluoro‐3‐methyl‐3‐silathiane

Abstract

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 13 C NMR spectroscopy and theoretical calculations. The conformer ratio at 103 K was measured to be about 5 ax :5 eq ¼ 15:85, 6 ax :6 eq ¼ 50:50 and 7 ax :7 eq ¼ 25:75. The equatorial preference of the methyl group in 5 (0.35 kcal mol S1 ) is much less than in 3-methylthiane 9 (1.40 kcal mol S1 ) but somewhat greater than in 1-methyl-1-silacyclohexane 1 (0.23 kcal mol S1 ). Compounds 5-7 have low barriers to ring inversion: 5.65 (ax ! eq) and 6.0 kcal mol S1 (eq ! ax) (5), 4.6 kcal mol S1 (6), 5.1 kcal mol S1 (Me ax ! Me eq ), and 5.4 kcal mol S1 (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

Conformational properties of 1-cyano-1-silacyclohexane, C5H10SiHCN: Gas electron diffraction, low-temperature NMR and quantum chemical calculations

“…Whereas a solvation effect, possibly related to the polarity of the cyano group, we note that continuum solvation calculations, by using both the COSMO 43 and SMD 44 solvation models (implicit solvation models), were carried out separately at the B3LYP give positive A values both in gas-phase and in solutions. In this context, however, it is notable that some 1-methyl-3-hetero(X)-1-silacyclohexanes (X = NMe, 56 O, 57 and S 58,59 ) also show Me-axial preferences in the gas-phase (GED) but Me-equatorial preferences by DNMR in solutions.…”

Synthesis and conformational properties of 1,3-dimethyl-3-phenyl-1,3-azasilinane. Low temperature dynamic NMR and computational study

“…The relevant fractions were combined and the solvents removed under reduced pressure to give 1 in 58% yield as a colorless viscous liquid. 1 H and 13 C NMR data are given in Table 1. …”

“…In the room temperature 13 C NMR spectrum each carbon atom is represented by a single line. Due to the presence of the chiral silicon center in the molecule, protons of methylene groups are diastereotopic: at 273 K, the 4-CH A and 4-CH B resonate separately at 0.85 and 1.00 ppm as multiplets of 8 lines each, the 5-CH 2 group exhibiting a very complex multiplet at about 2.00 ppm, the 2-CH 2 group proves to be an AB system at 2.10 and 2.15 ppm, respectively, and the 6-CH are not present due to the dihedral angle dependence of the vicinal 3 J(C,H) coupling as origin for the cross peaks.…”

“…Solvents were freshly distilled from the appropriate drying agents immediately before use (diethyl ether, sodium benzophenone ketyl; benzene, CaH 2 ). The 1 H, 13 C, and 29 Si NMR spectra were recorded on a Brucker DPX 400 spectrometer ( The HRMS ESI spectra were recorded using a Micromass Q-TOF micro mass spectrometer in positive electrospray mode. All samples were injected (10µL/min) with a Harvard syringe pump.…”

“…1,3-azasilinanes. 10 We also prepared 3-X-3-Me-1,3-thiasilinanes (X = H, F) from 3-Me-3-Ph-1,3-thiasilinanes 12 in order to study the conformational behavior of the latter thiasilinanes 13,14 as well as of 3-Me-3-Ph-1,3-thiasilinane itself. 14 It is a general rule that monosubstituted cyclohexanes prefer the equatorial conformation because of unfavorable 1,3-diaxial interactions in the axial conformation.…”