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Title: Temperature and solvent-dependent coupling constants in ESR spectroscopy
Author: Howard, C. B.
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1975
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This thesis is concerned with dynamic effects on the couplings of e.s.r. spectra. The cation radicals of 1,2,4,5-benzenetetrol, 1,4-diaminobenzene and diaminodurene were prepared and their e.s.r. couplings in solution were determined over a wide range of temperature. The couplings of the first two species were analysed in terms of McLachlan MO calculations and the temperature dependences of the hydroxyl proton and amino proton and 14N couplings were analysed in terms of hindered internal rotation of these groups using Mathieu functions. The barriers to rotation were found to be 24 ± 2 and 9.9 ± 0.8 kJ mol⁻¹ respectively. Values found for the δ-π parameters 0H/0h and QH/CNH were -3.87 ± 0.05 and +3.80 ± 0.20 mT respectively. In all three species, hindered internal rotation simply results in a redistribution of spin density between the functional group and the attached ring carbon atom. Spin densities at the other carbon atoms are essentially constant. The temperature dependence of the ring proton coupling of 1,4-diaminobenzene was analysed in terms of out-of-plane vibrations using hyperbolic functions. The 14N coupling of di-t-butyl nitroxide was determined in a number of solvents, and the relationship of this quantity to various measures of solvent polarity was considered. The same quantity was measured in a number of mixtures of methanol and carbon tetrachloride over a range of temperatures. The variation of the coupling with solvent composition was analysed in terms of a hydrogen-bonded nitroxide/methanol complex, and the enthalpy of complex formation was found from the temperature dependence of the formation constant to be -6.7 ± 1.8 kJ mol⁻¹, a surprisingly low figure for the energy of a hydrogen-bond. Details of the theoretical background are given.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available