| Alkyl phenylglyoxylates provide excellent opportunities for mechanistic studies by the time-resolved infrared spectrometry technique. Their reactive intermediates possess appropriately long lifetimes, and the molecules have two carbonyl groups (benzoyl and ester) that have different infrared frequencies. In addition, the structural changes and excitations involve the diketoester moiety thus affecting the carbonyl groups' absorptions thereby providing rich information on the transient species present in the system.; The procedures for obtaining and processing time-resolved infrared spectra were developed. Most of the intermediates postulated in the mechanism of the photochemical decomposition of alkyl phenylglyoxylate were confirmed by direct observation in time-resolved infrared spectra.; The measured rate constants were higher than the values obtained from UV-vis laser flash photolysis experiments, and they also depended linearly on the excitation energy. The rate constants extrapolated to zero energy were very close to the UV-vis data. Structure-reactivity relationships were in agreement with those previously reported. Also, in agreement with literature, the kinetic isotope effects were absent or small.; Indications of the bimolecular pathway leading to the ketene formation were found. Also, evidence in favor of the Norrish Type I process occurring in alkyl phenylglyoxylates was obtained. |
