Photoreaction mechanism of 2-chloropropionic acid in a low-temperature argon matrix

The photoreaction mechanism of 2-chloropropionic acid in a low-temperature argon matrix has been investigated by Fourier transform infrared spectroscopy with an aid of density-functional-theory calculations. The photoisomerization from syn to anti around the C-O bond with the isomerization around the central C-C bond was observed when the matrix sample was exposed to UV light (lambda > 240 nm). In the anti isomer produced in this reaction, the hydrogen atom in the carboxyl group is so close to the chlorine atom that this isomer changed to a less stable photoreaction intermediate by elimination of HCl. The photoreaction intermediate, which showed a strong C=O stretching band around 1910 cm(-1), was assigned by comparison with the calculated spectral pattern to methyloxiranone, a 3-membered lactone. This photoreaction mechanism was confirmed by a kinetic analysis for the absorbance changes of the reactant and intermediate bands. (c) 2007 Elsevier B.V. All rights reserved.