The presence of the double bond affects the reaction rate constant
of ketone with OH, as can be observed from Fig. 18 which
presents the rate constant of 2-butanone and 3-buten-2-one with
OH. The reaction rate of 3-bute-2-one + OH is about 30–40% slower
than that of 2-butanone + OH. This difference can be attributed to
the presence of the double bond which forces 3-buten-2-one to
have two less hydrogen atoms compared with 2-butanone. Thus
the available H-abstraction sites are reduced and the overall ketone
+ OH rate decreases. Additionally, the vinyl hydrogen atoms are
harder to abstract than the alkyl ones. This is similar to the difference
between OH + alkene and OH + alkane rates, where the former
is much slower [34,52,53,55,56]. In order to gain a further
understanding of the influence of double bonds and carbonyl
groups on ignition times and reaction rates, experiments with
higher order and branched ketones are currently in progress in
our laboratory.