Theoretical Calculations of Optical Rotatory Strengths of Twisted Acrylaldehydes, (-)-Lactic Acids and Their Anions

Abstract

The reduced optical rotatory strengths (γ -ORS's) of twisted acrylaldehydes, (-) -lactic acids and their anions were calculated by means of the transformation technique of overlap integral, where the wave functions obtained by the CNDO/2 method were applied and the effects of configuration interaction were taken into account, The calculated valuse for the transoid (θ =10° ) of the twisted acrylaldehyde well fit the empirical Djerassi-Snatzke's rules, while that for cisoid (θ =170° ) is reverse of the result predicted by the empirical rules in sign, although its intensity is weak (Table 1). The present calculations reveal that the Djerassi-Snatzke's rule has many exceptions. In the case of the π -π r* transitions of the (-)-lactic acids some rotamers in which the intramolecular hydrogen bonds are formed, show negative γ -ORS, while the others have positive γ -ORS and high total energies (Table 2). Calculation for the anions of the (-)-la ctic acid shows that they do not give the results as seen in the (-)-lactic acids (Table 4). These facts are consistent with the CD spectra reported by Craig et al. (Table 3).