Photochemical generation and detection of an elusive rotamer of matrix-isolated mesityl oxide. Dispersive kinetics of the thermal isomerization: twisted s-trans→ s-cis forms

Abstract

The photochemical behaviour of mesityl oxide (4-methylpent-3-en-2-one) was investigated in a number of rare-gas matrices. A ‘new’ conformer, most probably the twisted s-trans form, generated by irradiation with UV light (λ_max 250 nm), was trapped and its UV and IR absorption spectra were recorded. The twisted s-trans isomer was unstable upon warming of the matrix and rearranged to starting material (s-cis isomer). Kinetic measurements of the twisted s-trans→ s-cis rotational isomerization were performed in an argon matrix in the temperature range 37–41 K, and these data were analysed in terms of dispersive kinetics with time-dependent rate coefficients.