Time-resolved ESR studies on ketyl type radical-amine complexes

Time-resolved (TR) ESR spectra were measured for alpha-hydroxybenzyl-amine (alpha-HB) and alpha-hydroxydiphenylmethyl-amine complexes. Hyperfine coupling constants (hfcc) of the complexes were determined, and considerable increase in hfcc was recognized on the hydrogen of hydroxy group of both radical complexes, which suggests that the complexes are produced through the hydrogen bond formation between hydroxy group df the radical and amino group of amines. Complex formation constants were determined for various alpha-HB-amine complexes by monitoring TR-ESR signals of the complexes against amine concentrations. It has been noticed that the degree of hydrogen substitution on nitrogen atom of aliphatic amine roughly determines the complex formation constant: complexes with primary amines show the largest value of the complex formation constant while tertiary amines show the smallest value. This result is interpreted based on the structure of the amine.