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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 6, Number 6
June 20, 1985 

Theoretical Studies on the Hydrogen Atom transfer Reaction (Ⅱ)
Ikchoon Lee, Chang Hyun Song, Byung Choon Lee
The hydrogen atom transfer reaction between substituted methane, CH3X, and its radical, CH2X(X = H, F, CH3, CN, OH and NH2) was studied by MINDO/3 method. The transition state(TS) structure and energy barriers were determined and variation of the transition state and of the reactivity due to the change of X were analyzed based on the potential energy surface characteristics. It was found that the greater the radical stabilization energy, the looser the TS becomes; the TS occurs at about 15% stretch of the C-H bond, which becomes longer as the radical stabilization energy of CH2X increases. The intrinsic barrier, ΔE≠ X,X, of the reaction with X was found to increase in the order H < F < CH3 < CN < OH < NH2. The degree of bond stretch of the C-H bond at the TS also had the same order indicating that the homolytic bond cleavage of the C-H bond is rate-determining. Orbital interalictions at the TS between LUMO of the fragment C---H---C and the symmetry adapted pair of nonbonding, n±(n1±n2), or pi orbitals of the two X atoms were shown to be the dominant contribution in determining tightness or looseness of the TS. The Marcus equation was shown to apply to the MINDO/3 barriers and energy changes of the reaction.
362 - 366
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