Substituent effects on the disproportionation—combination rate constant ratios for gas‐phase halocarbon radicals, Part 5: Reactions of CF 3 + CF 3 CH 2 CHCH 3 and CF 3 CH 2 CHCH 3 + CF 3 CH 2 CHCH 3

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 CH 2 position of the CF 3 CH 2 CHCH 3 radical and as 0.24 ± 0.03 when the H is removed from the CH 3 position in the reaction with the CF 3 radical. For the self‐reaction between two CF 3 CH 2 CHCH 3 radicals, k d / k c has been measured as 0.27 ± 0.03 when the H is removed from the CH 2 position and as 0.47 ± 0.04 when the H is removed from the CH 3 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 CF 3 and 0.54 when CF 3 CH 2 CHCH 3 is the acceptor radical. Branching fraction results show that the CF 3 substituent on the CF 3 CH 2 CHCH 3 radical hinders disproportionation when CF 3 is the acceptor radical. When the accepting radical is CF 3 CH 2 CHCH 3 the CF 3 substituent may slightly impede the disproportionation reaction, but the branching ratio is nearly statistical. The effect of substituents on the donor radical, CF 3 CH 2 CHX, will be discussed for the series X = H, CF 3 , Cl, and CH 3 when the acceptor radical is CF 3 . © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 549–557, 2001