Substituent effects on the disproportionation-combination rate constant ratios for gas-phase halocarbon radicals, part 5:: Reactions of CF3+CF3CH2CHCH3 and CF3CH2CHCH3+CF3CH2CHCH3

Rate constant ratios, k(d)/k(c) for the disproportionation/combination reaction have been measured as 0.07 +/- 0.02 when an H is removed from the CH2 position of the CF3CH2CHCH3 radical and as 0.24 +/- 0.03 when the H is removed from the CH3 position in the reaction with the CF3 radical. For the self-reaction between two CF3CH2CHCH3 radicals, k(d)/k(c) has been measured as 0.27 +/- 0.03 when the H is removed from the CH2 position and as 0.47 +/- 0.04 when the H is removed from the CH3, position. The branching fraction, corrected for the number of hydrogens at each site, is 0.70 favoring the methyl position when the acceptor radical is CF3 and 0.54 when CF3CH2CHCH3 is the acceptor radical. Branching fraction results show that the CF3 substituent on the CF3CH2CHCH3 radical hinders disproportionation when CF3 is the acceptor radical. When the accepting radical is CF3CH2CHCH3 the CF substituent may slightly impede the disproportionation reaction, but the branching ratio is nearly statistical. The effect of substituents on the donor radical, CF3CH2CHX, will be discussed for the series X = H, CF3, Cl, and CH3 when the acceptor radical is CF3. (C) 2001 John Wiley & Sons, Inc.