IR-induced photorotamerization of propanal and 3-chloropropanal in low-temperature matrices. Ab initio optimization of conformer geometries, and calculation of torsional barrier heights

Abstract

Propanal and 3-chloropropanal have been studied in solid Ar and N 2 matrices. A fast IR-induced cis → gauche process was found for propanal, whereas the reverse process occurred in the dark upon warming the matrices. A very fast process was found for 3-chloropropanal in Ar; in N 2 it was 60 times slower. The reverse process occurred upon warming in the dark also for this compound. Ab initio calculations were carried out for both compounds at the 4–31G level, and the results were used in interpreting the experimental results. Geometries of the conformers were fully optimized and torsional potential-energy barrier heights calculated.