NUCLEAR-SPIN-LATTICE RELAXATION-TIMES IN THE RADICAL CATIONS OF METHOXYBENZENES - A FLASH CIDNP STUDY

The T1-times of the aromatic protons in the radical cations of 1,2- an d 1,3-dimethoxybenzene, and 1,2,3- and 1,3,5-trimethoxybenzene have be en determined as functions of temperature by time resolved measurement s of chemically induced dynamic nuclear polarization (''flash CIDNP'') . The results are discussed with the Solomon-Bloembergen theory. The d ipolar interaction between proton spin and magnetic moment of the unpa ired electron was identified as the predominant source of relaxation. A direct proportionality was found between the slopes of plots of 1/T1 as a function of the rotational correlation time tau(r), and the squa red hyperfine coupling constants of the observed protons. This is expl ained by a simple molecular orbital model. Calculations taking into ac count the electron distribution gave a satisfactory agreement between experimental and theoretical values of partial derivative(1/T1)/partia l derivative tau(r).