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

Abstract

The low temperature (95 K) NMR study of 1-Ph-1-t-Bu-silacyclohexane (1) showed the conformational equilibrium to be extremely one-sided toward thePhax,t-Bueq conformer. The barrier to interconversion has been measured (4.2–4.6 kcal/mol) and the conformational equilibrium [Δν = 1990.64 ppm (29Si), 618.9 ppm (13C), 1-Phax:1-Pheq = (95.6–96.6%):(3.4–4.4%), K = 25 ± 3, ΔG° = −RT ln K = 0.58–0.63 kcal/mol] analyzed. The assignment and quantification of the NMR signals is supported by MP2 and DFT calculations.

Nuclear Magnetic Resonance

“…126 Kleinpeter and Koch employed NICS calculation for testing the nature of carbon-boron bond in boron trapped N-heterocyclic carbenes. 127 In addition, Kleinpeter et al 128 reported on a 29 Si and 13 C NMR conformational equilibrium study of 1-phenyl-1-tert-butylsilacyclohexane. Jakubowska and Pecul 129 characterized nuclear magnetic shieldings of Zn 2 , Cd 2 and Hg 2 dimers with relativistic four-component Dirac-Coulomb hamiltonian.…”