Use this URL to cite or link to this record in EThOS:
Title: Thermochemistry of cyclic and acyclic radicals and kinetics of their recombination reactions
Author: Guiver, Steven Charles
ISNI:       0000 0001 3522 0992
Awarding Body: Open University
Current Institution: Open University
Date of Award: 1987
Availability of Full Text:
Access from EThOS:
Access from Institution:
The thermochemistry of a series of acyclic and cyclic hydrocarbon radicals has been studied using a radical buffer technique in solution. From these studies radical heats of formation and hydrocarbon carbon-hydrogen bond dissociation energies have been determined. These results are consistent with an increase in hydrocarbon bond dissociation energies over the previously accepted values with D(C2H5-H) = 419 kJmol-1, D(n-C3H7-H) = 418 kJmol1-, D(i-C3H7-H) = 404 kJmol-1, D(c-C5H9-H) = 402 kJmol-1, D(c-C6H11-H) = 420 kJmol-1 and D(c-C7H13-H) = 400 kJmol-1. The work suggests typical primary carbon-hydrogen bond dissociation energies of 420 kJmol-1 and typical secondary carbon-hydrogen bond dissociation energies of 400 kJmol-1, although an anomalous result is obtained for cyclohexane. The high value obtained for D(c-C6H11-H) is more typical of a primary than a secondary bond, a result which is considered in terms of ring strain and eclipsing interactions occurring upon formation of cycloalkyl radicals. Further gas phase studies of the radical buffer reaction allowed relative radical recombination rate constants to be determined for cyclopentyl and cyclohexyl radicals. From these studies the rate constant for cyclopentyl radical recombination was determined as 2.4 x 109 lmol-1s-1 and the rate constant for cyclohexyl radical recombination as 1.6 x 109 lmol-1s-1, both at 430K. These results are consistent with radical recombination in the gas phase being collision controlled and are considered in the context of previous suggestions that the cyclohexyl radical recombination rate constant is more than two orders of magnitude lower than that for cyclopentyl recombination.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Free radical thermochemistry