Veronica L. Vogel

The mechanisms of spin delocalization through sigma bonds delocalization to gamma protons [1]

A study of the mechanisms of spin delocalization to γ hydrogens was conducted by investigating the change in spin density distribution upon geometrical deformation. The mechanisms are expressed in valence bond pictures. The spin densities were calculated using the SCF-MO-INDO method for the propyl radical. An empirical expression for γ-hydrogen hfscs is proposed.

A theoretical analysis of the temperature dependence of the E.P.R. spectrum of bis(trifluoromethyl) nitroxide

Self-consistent field calculations using the INDO approximation have been performed for many trial geometries of bis(trifluoromethyl) nitroxide. It has been found that the structure of minimum energy is non-planar at the nitrogen atom with a very low barrier to inversion. It is concluded that an increased amplitude of vibration of the molecule away from planarity with increased temperature is the only appropriate way to account for the temperature dependence of the E.S.R. spectrum of the radical.

Effect of Charge on the EPR Hyperconjugative Interaction Parameter

Extensive McLachlan MO calculations have been performed on a number of methyl‐substituted radicals and radical ions to obtain a consistent set of parameters to describe the methyl group and to examine the effect of charge density on the parameter QCCH3H which relates the methyl hfsc (hyperfine splitting constant) to the spin density. It was found that there was a strong dependence of QCCH3H on charge, but it was concluded that other factors were involved and that caution should be exercised when employing β‐hydrogen hfscs as a measure of spin density.