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
- 30 April 2005
- journal article
- research article
- Published by American Chemical Society (ACS) in The Journal of Physical Chemistry A
- Vol. 109 (20), 4540-4551
- https://doi.org/10.1021/jp040735g
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).Keywords
This publication has 61 references indexed in Scilit:
- Comparisons between Density Functional Theory and Conventional ab Initio Methods for 1,2-Elimination of HF from 1,1,1-Trifluoroethane: Test Case Study for HF Elimination from FluoroalkanesThe Journal of Physical Chemistry A, 2002
- Ab Initio Rate Constants for Unimolecular Reactions: Eliminations of HX from CH3CH2X and DX from CD3CD2X (X = Cl, Br)The Journal of Physical Chemistry A, 2002
- Vibrationally Mediated Photodissociation of Jet-Cooled CH3CF2Cl: A Probe of Energy Flow and Bond Breaking DynamicsThe Journal of Physical Chemistry A, 2002
- Unimolecular Reaction Kinetics of CF2ClCF2CH3 and CF2ClCF2CD3: Experimental Evidence for a Novel 1,2-FCl Rearrangement PathwayThe Journal of Physical Chemistry A, 2001
- Rotational spectrum, internal rotation barrier and ab initio calculations on 1-chloro-1-fluoroethaneThe Journal of Chemical Physics, 1996
- Transition State for 1,2 Hydrogen Halide Elimination from Ethyl HalidesThe Journal of Physical Chemistry, 1994
- Collisional energy transfer in the two-channel thermal unimolecular reaction of chloroethane-1,1,2-d3The Journal of Physical Chemistry, 1994
- Torsional spectra of molecules with two C3v rotors—XXV. Rotational and vibrational spectra, r0 structure, barriers to internal rotation and ab initio calculations for 2,2-difluoropropaneSpectrochimica Acta Part A: Molecular Spectroscopy, 1993
- Far infrared and low frequency gas phase Raman spectra and conformational stability of the 1-halopropanesThe Journal of Chemical Physics, 1984
- The Thermal Unimolecular Decompositions of CH3CD2Cl, CD3CD2Cl, and CH3CHCl2Berichte der Bunsengesellschaft für physikalische Chemie, 1978