Conformational analysis of 1-chloro- and 1-bromo-2-propanol.

The conformational isomerism of 1-chloro- (1) and 1-bromo-2-propanol (2) was theoretically and spectroscopically (NMR) analyzed. Conformers with the X-C-C-O (X = Cl and Br) fragment in the gauche orientation were found to be strongly prevalent both in the gas phase and solution, as analyzed by means of coupling constants in the diastereotopic methylene hydrogens. The gauche effect was calculated to be due to hyperconjugation rather than intramolecular X center dot center dot center dot HO hydrogen bond, indicating the rule of the stereochemical control in compounds with motifs (halohydrins) widely found in pharmaceutical and agrochemical products and intermediates.