Comparative study of structure and photo-induced reactivity of malonaldehyde and acetylacetone isolated in nitrogen matrices

Abstract

The structure and reactivity of the eight enolic forms (one chelated and seven non-chelated) of malonaldehyde and acetylacetone are compared through theoretical and experimental data. Ground-state geometries, energies, and vibrational frequencies are calculated with the B3LYP∕6–311++G(2d,2p) model chemistry. The electronic delocalization as well as the cis/trans rotamer properties are analyzed. The hydrogen bond strength of the chelated forms can be estimated by the energy difference between chelated and non-chelated forms, and its enhancement due to methyl-induced electron release is estimated as 1.7kcal∙mol−1. UV- and IR-induced reactivity of molecules isolated in nitrogen matrices is studied by means of FT-IR spectrometry. Interconversion between rotamers is the main process observed for both molecules, only some among the seven non-chelated forms being created.