P. Dokolas et al., Reaction of acyclic hydrocarbons towards t-butoxy radicals. A study of hydrogen atom abstraction by using the radical trapping technique, AUST J CHEM, 51(12), 1998, pp. 1113-1120
The reaction of 3-methylpentane and 2,4-dimethylpentane toward t-butoxy rad
icals has been investigated, in neat and benzene solutions, by using the ra
dical trapping technique. Abstraction occurs principally from the tertiary
and secondary C-H reaction sites of 3-methylpentane and the tertiary positi
on of 2.4-dimethylpentane. The tertiary and in particular secondary C-H rea
ction sites of 2,4-dimethylpentane are shown to be considerably less suscep
tible towards t-butoxy radical facilitated abstraction compared with the eq
uivalent reaction sites of 3-methylpentane. As a result, the latter is thre
e times as reactive as 2,4-dimethylpentane as a neat hydrocarbon solution a
nd seven times as reactive in a diluted mixture of benzene. Differences in
selectivity and rate of hydrogen abstraction, between the substrates, are i
nterpreted in terms of non-bonding interactions retarding t-butoxy radicals
from approaching sterically demanding C-H reaction sites. The selectivity
from 3-methylpentane is solvent-insensitive whereas abstraction from 2,4-di
methylpentane is modified in benzene. Further, the rate of hydrogen abstrac
tion, from either substrate, to t-butoxy radical beta-scission is considera
bly smaller in benzene. Both observations are interpreted in terms of t-but
oxy radical solvation by the aromatic solvent.