Unimolecular rate constants for HX or DX elimination (X = F, Cl) from chemically activated CF3CH2CH2Cl, C2H5CH2Cl, and C2D5CH2Cl: threshold energies for HF and HCl elimination.

TitleUnimolecular rate constants for HX or DX elimination (X = F, Cl) from chemically activated CF3CH2CH2Cl, C2H5CH2Cl, and C2D5CH2Cl: threshold energies for HF and HCl elimination.
Publication TypeJournal Article
Year of Publication2005
JournalThe journal of physical chemistry. A
Volume109
Issue20
Pagination4540-51
Date Published2005
ISSN1089-5639
Abstract

Vibrationally activated CF(3)CH(2)CH(2)Cl molecules were prepared with 94 kcal mol(-1) of vibrational energy by the combination of CF(3)CH(2) and CH(2)Cl radicals and with 101 kcal mol(-1) of energy by the combination of CF(3) and CH(2)CH(2)Cl radicals at room temperature. The unimolecular rate constants for elimination of HCl from CF(3)CH(2)CH(2)Cl were 1.2 x 10(7) and 0.24 x 10(7) s(-1) with 101 and 94 kcal mol(-1), respectively. The product branching ratio, k(HCl)/k(HF), was 80 +/- 25. Activated CH(3)CH(2)CH(2)Cl and CD(3)CD(2)CH(2)Cl molecules with 90 kcal mol(-1) of energy were prepared by recombination of C(2)H(5) (or C(2)D(5)) radicals with CH(2)Cl radicals. The unimolecular rate constant for HCl elimination was 8.7 x 10(7) s(-1), and the kinetic isotope effect was 4.0. Unified transition-state models obtained from density-functional theory calculations, with treatment of torsions as hindered internal rotors for the molecules and the transition states, were employed in the calculation of the RRKM rate constants for CF(3)CH(2)CH(2)Cl and CH(3)CH(2)CH(2)Cl. Fitting the calculated rate constants from RRKM theory to the experimental values provided threshold energies, E(0), of 58 and 71 kcal mol(-1) for the elimination of HCl or HF, respectively, from CF(3)CH(2)CH(2)Cl and 54 kcal mol(-1) for HCl elimination from CH(3)CH(2)CH(2)Cl. Using the hindered-rotor model, threshold energies for HF elimination also were reassigned from previously published chemical activation data for CF(3)CH(2)CH(3,) CF(3)CH(2)CF(3), CH(3)CH(2)CH(2)F, CH(3)CHFCH(3), and CH(3)CF(2)CH(3). In an appendix, the method used to assign threshold energies was tested and verified using the combined thermal and chemical activation data for C(2)H(5)Cl, C(2)H(5)F, and CH(3)CF(3).

URLhttps://dx.doi.org/10.1021/jp040735g
DOI10.1021/jp040735g
Short TitleJ Phys Chem A
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