The reaction of 3-methylpentane and 2,4-dimethylpentane toward t-butoxy
radicals has been investigated, in neat and benzene solutions, by using the
radical trapping technique. Abstraction occurs principally from the tertiary
and secondary C-H reaction sites of 3-methylpentane and the tertiary position
of 2,4-dimethylpentane. The tertiary and in particular secondary C-H reaction
sites of 2,4-dimethylpentane are shown to be considerably less susceptible
towards t-butoxy radical facilitated abstraction compared with the equivalent
reaction sites of 3-methylpentane. As a result, the latter is three times as
reactive as 2,4-dimethylpentane as a neat hydrocarbon solution and seven times
as reactive in a diluted mixture of benzene. Diferences in selectivity and
rate of hydrogen abstraction, between the substrates, are interpreted 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-dimethylpentane is
modified in benzene. Further, the rate of hydrogen abstraction, from either
substrate, to t-butoxy radical β-scission is considerably smaller in
benzene. Both observations are interpreted in terms of t-butoxy radical
solvation by the aromatic solvent.
Acyclic hydrocarbons and ketones in cold-seep carbonates from central Hokkaido, northern Japan
