ESR spectra, structure and photochemistry of carboxylic acid and ester anions: matrix isolation study

Using photo-induced electron transfer technique, anion radicals of carboxylic acids (CH3)n(= 0,1,2,3)CH3-nCOOH and their ethyl esters were generated in argon matrices and examined by ESR. The study confirmed the previously reported photolysis path A for both the acid and ester anions, and revealed the presence of the second photolysis path B, an intramolecular abstraction. where R = ethyl or H. Both reaction paths are effected by visible light (λ =450 nm). Reaction path A prevailed for the ethyl ester anions, while reaction path B generally prevailed for the acid anions. For (CH3)3CCOOH anions, the intramolecular abstraction involving a γ proton was observed. The conformations (the pyramidal shape and the azimuthal position of the β alkyl group) and the unpaired electron distributions of the acid and ester anions given by the AM1-MNDO molecular orbital method are in excellent agreement with those deduced from the ESR spectra observed at 4 K.