INFRARED-SPECTRA AND THEORETICAL-STUDY OF THE CONFORMATIONS OF SUBSTITUTED BENZOYLKETENE-S,S-ACETALS

The C=O stretching frequencies of substituted benzoylketene-S,S-dimeth ylacetals (1a-1o) and benzoylketene-S,S-ethyleneacetals (2a-2m) were m easured in CHCl3 and CCl4 and correlated with the Hammett substituent constants. The correlations were split into two different and well sep arated lines for compounds containing electron donor and electron acce ptor substituents, which were assigned to s-trans and s-cis quasiplana r conformations. The correlations of carbonyl stretching frequencies w ith C=O bond orders and oxygen atom charge densities calculated using the semiempirical AM1 method reveal similar results consistent with as signments of structures 1 and 2 to two quasiplanar conformations. The preparation of some new benzoylketene-S,S-acetals is reported as well.