Investigation of the near-degeneracy effects of the mono-alkyl substituted benzenes by ESR and ENDOR

Author.In the first chapter, we introduce the theory of ESR and ENDOR spectroscopy. In the second chapter, a description is given of the ESR and ENDOR spectrometers used in our measurements, also included is the sample preparation technique. Chapter three gives an outline of the Huckel and Mclachlan molecular orbital theory used in this thesis. We also discuss the mechanism of proton hyperfine coupling. The effect of alkyl substitution in the lifting of the degeneracy of benzene and the possible explanation of the resulting spin densities, such as the thermal mixing, Jahn-Teller and vibronic effects. In chapter four, we present the results of our ESR and ENDOR measurements on a number of mono-alkyl substituted benzenes. Proton hyperfine splitting constants of toluene, ethyl, n-propyl, n-butyl, n-amyl, iso-propyl, sec-butyl, t-butyl benzenes, 1-phenyl hexane and 1-phenyl heptane are reported. The results are discussed in the light of spin density calculations using the HMO and Mclachlan methods and compared with other calculations found in the literature. Estimations of the mining between the two lowest antibonding states have been made. Finally, temperature dependence of some of the splittings were measured in an attempt to determine the importance of the thermal contribution of the mixing