Vibrational Effects on the Hyperfine Interactions of Aromatic Radicals in Solution

Measurements of the temperature dependence of the proton hyperfine coupling constants of a number of aromatic radicals in solution together with some measurements of the proton-to-deuteron coupling constant ratio are reported. These and data from the literature show the effects of out-of-plane CH vibrations. A relationship between the two types of measurements is demonstrated. Such vibrations lead to a small hyperfine coupling between the proton and spin densities on carbons adjacent to the one to which it is bonded. The implications of this effect are discussed.