Stereochemical Consequences of Halogen Atom Substitution. 1. Rotational Conformer Effects in Gaseous Diastereomeric 2,3-Dihalobutanes

Article abstract of DOI:10.1021/j100369a023

The stereochemical consequences of translationally excited ³⁸Cl-for-X (X = F, Cl) substitution in (2S,3R)-meso- and (2S,3S)-dl-difluorobutane, (2S,3R)-dl- and (2S,3R)-dl-chlorofluorobutane, and (2S,3R)-meso- and (2S,3S)-dl-dichlorobutane were studied in the gas phase.Although retention of configuration was determined to be the dominant substitution pathway, substantial inversion product yields were observed in all cases.A comparison of these yields revealed that the (S,R) configuration within each set always gave a smaller yield of the inverted product than the (S,S) configuration.This observation was consistent with the hypothesis that back-side substitution was a direct mechanism and that steric hindrance to such attack was subject to differences in the rotational conformer populations within each substrate configuration.In contrast, the measured yields of retention products were insensitive to substrate configuration.