I. Studies of the Spin Distribution in Aromatic Radicals. II. Electron Resonance Studies of Some Sandwich Compounds

Citation

Dearman, Henry Hursell (1960) I. Studies of the Spin Distribution in Aromatic Radicals. II. Electron Resonance Studies of Some Sandwich Compounds. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/CA5W-J786. https://resolver.caltech.edu/CaltechETD:etd-03142006-142740

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Part I: Studies of the Spin Distributions in Aromatic Radicals. It is shown that if conventional molecular orbital theory is extended in such a way as to include electron correlation, according to the proposal of Lowdin, negative spin density is predicted at unstarred positions of odd alternant hydrocarbon radicals. However, it is found that Lowdin's suggested method of alternant orbitals is not a sufficiently good approximation to the ground state of an even alternant hydrocarbon ion for the effects of electron correlation on the [...] electron spin density to be estimated. As a check of the validity of this approximate wave function for the radicals, the method of alternant orbitals function for the allyl radical is developed and commpared numerically with the results of a [...] configuration calculation. Calculation of spin densities by simple valence bond theory is described for several odd alternant radicals. For the perinaphthenyl and trivinylmethyl radicals, the secular equation is solved and the ground state eigenvector is derived. Normalization gives the coefficients of the various structures for the benzyl, [alpha]-methylnaphthanyl and [beta]-methylnaphthanyl radicals from the coefficient ratios given by Pauling and Wheland. Equations are derived which relate the [...] electron spin density at an atom in the [...] molecular framework in that hyperfine coupling constant due to the atom itself. Previously, McConnell and Chesnut have shown that there is a linear relation between the proton coupling constant and the [...] electron spin density at the adjacent carbon atom in [...] molecular radicals. In the case of the coupling constant of the carbon atom itself, for instance, it is shown that the relation is also a linear one, but the spin density at any neighbor atom must be included. It is concluded that negative spin density at a neighbor results in "donation" of spin density to the atom in question and to the observation of an abnormally large coupling constant. Estimation of the necessary constants for C13 is carried out semi-empirically in a simple way. Part II. Electron Resonance studies of Some Sandwich Compounds. ESR signals from pure polycrystalline nickelocene and cobaltocene are observed at liquid temperature. Although little information of a quantitive nature can be obtained from a powder spectrum, comparison with the predictions of Robertson is made whenever possible. The ESR spectrum of vanadocene as a substitutional impurity in a single crystal of ferrocene at room temperature is measured. The angular dependence of the absorption peaks is interpreted using the spin Hamiltonian given by Schulz-Du Bois for the isoelectronic ion, Cr+3. This analysis allows the evaluation of the splitting of the ground quartet which is present in the zero magnetic field, [...] = 50 Kmc.

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