Photochemistry of the matrix-isolated α,β-unsaturated aldehydes acrolein, methacrolein and crotonaldehyde at 4.2 K

The UV photolysis of the α,β-unsaturated aldehydes acrolein, methacrolein and crotonaldehyde in argon matrices at λ > 300 nm has shown a major photochemical deactivation pathway to be conformational isomerism to the thermodynamically less stable s-cis form. This type of isomerization may account for the rapid internal conversion observed in the gas phase. Matrix-isolated crotonaldehyde undergoes further isomerization to ethylketene and enol-crotonaldehyde, as observed in the analogous gas-phase photolysis. In addition, another H-abstraction product was detected (νOH= 3674 cm–1) which is probably derived from the photolysis of s-cis-crotonaldehyde. At shorter excitation wavelengths (λ > 230 nm) acrolein and methacrolein isomerize to methyl–ketene and dimethylketene, respectively.