Spectroscopy and photochemistry of phenylacetic acid esters and related substrates. The stereoelectronic dependence of the aryl/carboxyl bichromophore interaction

Article abstract of DOI:10.1021/jo00089a025

The 254-nm-initiated Norrish Type II photofragmentation of the ethoxyethyl esters of a series of phenylacetic acids (1b-4b) has been studied in order to further elaborate the aryl/ester interaction that is photochemically and photophysically evident in these systems. The ethoxyethyl ester of benzonorbornene-1-carboxylic acid (5) has also been prepared and studied, as has a rigid tricyclic lactone (6) which places the chromophores in an optimal stereoelectronic relationship for interaction. The experimental work is accompanied by Hartree-Fock (HF), Natural Bond Orbital (NBO), and Configuration Interaction with Single Excitations (CIS) calculations on the methyl esters of phenylacetic acid (1a) and α-methoxyphenylacetic acid (4a). The calculations confirm extensive through-space (TS) and through-bond (TB) interactions between the aryl and ester π* orbitals but fail to provide conformational or electronic arguments to explain the unusually high reactivity of the α-methoxy series.