Electron Spin Resonance of Anion Radicals of Aromatic Esters. I. The Anion Radicals of Methyl, Ethyl and Isopropyl Benzoates, and of Methyl and Ethyl Isonicotinates

The ESR spectra of the anion radicals of methyl, ethyl and isopropyl benzoates, and of methyl and ethyl isonicotinates were observed. When the spin densities of these anions were calculated by using McLachlan’s method, the results were in good agreement with the experimental data. It has been found that the electron-withdrawing effect of the ester group is situated between those of the cyano and acetyl groups, and that the ester group may be locked into the benzene plane. Comparatively large splittings due to the α-protons in the ester group were observed. The proton position is defined by the notation: (Remark: Graphics omitted.) An equation, aCH3H=QOCH3Hρoπ, was assumed, and for these anion radicals values of |QOCH3H| much larger than 27.2 gauss for the C–CH3 hyperconjugation were evaluated.