ESR Spectra of Some Amino Acid Derivatives of Semiquinone Anions

Reaction of then-butyl esters of alanine and leucine with bothtert-butyl-1,4-benzoquinone and 1,4-naphthoquinone gave the correspondingN-substituted quinones. Substitution at both C-5 and C-6 was observed with 2-tert-butyl-1,4-benzoquinone, but C-6 substitution predominated. Reduction of the latter isomers and of the naphthoquinones gave ESR spectra to which splitting constants were assigned with the help of ENDOR spectroscopy and selective deuteration.