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, ¢E ) 0.0 ( 0.2 kcal/mol. Structural parameters (r0 and rs) 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.