Kinetic Studies of the Reactions of Alkyl and Silyl Hydrides Page: 56
ix, 125 leaves : ill.View a full description of this dissertation.
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56
10"n, and (2.7 ± 0.1) x 10'11 cm3 s"1, respectively. Combination of the rate constant values
with other information resulted in C-H bond strengths of 423.6 ± 2, 409.9 ± 2, and 405.1
± 2 kJ mol"1 for C2H5, i-C3H7, and t-C4H9, respectively. The rate constants measured and
the C-H bond enthalpies are in excellent agreement with the previous results by Seakins et
al.,61 and the discrepancies in C-H bond strength determined by different equilibria are
cleared. Arrhenius parameters of n-C3H7, (CH3)3Si with HBr have been investigated. From
these results, the primary C-H bond strength of propane and the tertiary Si-H bond
strength of trimethylsilane have been calculated to be 425.3 ± 3 and 397,8 ± 2 kJ mol"1.
The good agreement of the primary C-H bond strength in propane derived in this study
with Tsang's value25 which is determined by the association/dissociation equilibria justifies
the additivity/similarity principle in determining the rate constants of different steric types
of hydrogen abstraction in alkanes. The negative activation energies observed in the
reactions of HBr with n-propyl and trimethylsilyl radicals are consistent with the reaction
mechanism proceeding through a weakly bound intermediate complex. The bond strength
determination for alkanes and trimethylsilane confirms that methyl substitution decreases
the C-H bond energy in alkanes while it increases the Si-H bond energy in trimethylsilane.
These phenomena could be explained in terms of the inductive effect. The silyl-weakening
effect in silane is justified by the determination of the rate constant of reaction Si2H6 with
Br. The BDE in disilane is 12 kJ mol"1 less than in silane.
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Yuan, Jessie (Jessie Win-Jae). Kinetic Studies of the Reactions of Alkyl and Silyl Hydrides, dissertation, August 1996; Denton, Texas. (https://digital.library.unt.edu/ark:/67531/metadc277864/m1/67/: accessed July 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; .