SPECTROSCOPY AND PHOTOCHEMISTRY OF PHENYLACETIC ACID-ESTERS AND RELATED SUBSTRATES - THE STEREOELECTRONIC DEPENDENCE OF THE ARYL CARBOXYL BICHROMOPHORE INTERACTION/

The 254-nm-initiated Norrish Type II photofragmentation of the ethoxye thyl esters of a series of phenylacetic acids (1b-4b) has been studied in order to further elaborate the aryl/ester interaction that is phot ochemically and photophysically evident in these systems. The ethoxyet hyl ester of benzonorbornene-1-carboxylic acid (5) has also been prepa red and studied, as has a rigid tricyclic lactone (6) which places the chromophores in an optimal stereoelectronic relationship for interact ion. The experimental work is accompanied by Hartree-Fock (HF), Natura l Bond Orbital (NBO), and Configuration Interaction with Single Excita tions (CIS) calculations on the methyl esters of phenylacetic acid (1a ) and alpha-methoxyphenylacetic acid (4a). The calculations confirm ex tensive through-space (TS) and through-bond (TB) interactions between the aryl and ester pi orbitals but fail to provide conformational or electronic arguments to explain the unusually high reactivity of the a lpha-methoxy series.