Some Factors Which Affect the Spin Densitites of Protons, with Particular Emphasis on the β-Protons of Cyclobutenyl

Author: Steadman, Vivian Louise

Year: 1967

Degree: Master's thesis

Advisors: McLachlan, Andrew D.; McKoy, Basil Vincent

Committee Member: Unknown, Unknown

Option: Chemistry

DOI: 10.7907/6S0F-1650

Abstract

Both first-order and variational valence bond calculations were made to estimate the ESR hyperfine splittings of the β-protons of cyclobutenyl. The ESR spectrum of the radical has not been obtained; but on the basis of these calculations, it is anticipated that the β-proton splittings will be large and in the range 42g to 101g. The first-order results indicate considerably larger splittings than the variational calculation; this situation was shown to be in marked contrast with another valence bond calculation on a free radical containing β-protons. Possible inequality in the β-proton splittings of cyclobutenyl at low temperatures was also discussed.

The dependence of the spin densities of β-protons on π-electron excitation energies (in appropriate free radicals) was discovered and was shown to reduce the size of the β-proton hyperfine splittings. The agreement with experiment was satisfactory.

The transformation between the vector-coupling states for an eight electron system and its canonical states was obtained. The canonical states were found to be especially amenable to computer computations, involving the non-overlap, empirical valence bond theory.

The reasons for the suitability of the use of vector-coupling functions in configuration interaction in the valence bond theory were discussed. A case was presented in which it appeared desirable to distribute the antisymmetrical spatial components of the ground-state wave function somewhat differently in space than that of the symmetrical spatial components.

An anomaly in the ESR spectra of irradiated benzene was deduced from theoretical considerations.

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