AN ELECTRON SPIN RESONANCE STUDY OF THE PHOTOLYSIS OF CARBOXYLIC ACIDS, NEAT OR IN NON-POLAR SOLVENTS: REGIOSPECIFIC LOSS OF A HYDROGEN ATOM FROM THE α-POSITION

Article abstract of DOI:10.1039/P29850000385

When carboxylic acids RCH2CO2H (R = H, Me, Et, or Pr) are photolysed, either neat or in carbon tetrachloride, the e.s.r. spectra of only the radicals RC^.HCO2H are observed.Isobutyric acid Me2CHCO2H, similarly shows the spectrum of the radical Me2C^.CO2H at room temperature, but at lower temperatures the spectrum of the radical Me2C^.H can also be observed.Pivalic acid Me3CCO2H, shows only the spectrum of the Me3C^. radical.This is in contrast to the behaviour of the acids in polar solvents, when they normally show Norrish I cleavage of the alkyl-acyl bond, or photoreduction by the solvent.Two models are considered, to account for the regiospecific formation of the radicals RC^.HCO2H.The first assumes that cleavage of a C-OH bond in a hydrogen-bonded dimer yields an HO^. radical which is hydrogen-bonded to a carbonyl group of the acid .>, and this species then undergoes reiospecific intramolecular transfer of α-H.The second assumes initial formation of the RCH2^. radical, which then abstracts hydrogen from a second molecule of acid.

Full text of DOI:10.1039/P29850000385

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