Conformational Study of Molecules with Asymmetric Isotopic Substitution. Ring Puckering of 1-Silacyclobutane-1-d1

Article abstract of DOI:10.1021/j100219a012

1-Silacyclobutane-1-d1, , has been prepared and its infrared spectra have been analyzed.Several ring-puckering transitions have been observed in the far-infrared region and sum and difference bands have been observed in the Si-H stretching region.A ring-puckering potential function which simultaneously fits the data for the d0, d1, and d2 isotopic forms has been determined.Calculation of the wave functions for the d1 molecule shows that each of the lowest two very nearly degenerate energy states (ν = 0 and ν = 1) corresponds to only one distinct molecular conformation.Similarly, the nearly degenerate ν = 2 and ν = 3 states are primarily restricted to specific conformations.Doublets observed for the Si-H and Si-D stretching bands, corresponding to stretches from equitorial or axial positions, confirm these calculations.Model calculations on related systems demonstrate that both a sufficiently large barrier height and an asymmetry of the kinetic energy expansions are necessary for the conformational separation according to vibrational states.Although the reduced masses of the conformers of 1-silacyclobultane-1-d1 differ by only 0.20 percent, this is enough to produce the observed conformational discrimination.