Structures and energetics of axial and equatorial 1-methyl-1- silacyclohexane

The structural differences and the relative energies for the axial and equatorial forms of 1-methyl-1-silacyclohexane have been obtained from the rotational spectra of the normal, ²⁹Si, and all ¹³C isotopologues of the axial and equatorial forms, observed by molecular beam Fourier transform microwave spectroscopy. The two species appear to have the same energy, within uncertainty limits, ΔE = 0.0 ± 0.2 kcal/mol. Structural parameters (r₀ and r_s) are given for the two forms. The main structural differences are discussed. Potential barriers for the methyl group internal rotations (V₃) have been determined for both conformers to be 1.26(1) and 1.48(2) kcal/mol for the axial and equatorial species, respectively.