Abstract
Hydrocarbons (chiefly the lower alkanes) have been fluorinated by a competitive method in a high vacuum, all glass, static system. Monofluorides
formed by hydrogen abstraction from pairs of reactants have been measured by gas
chromatography and ratios of A factors and activation energy differences found for
reactions of the type,
F• + RH —» HF + R•
Absolute A factors for (2) have been obtained by assuming that the A factor for
ethane calculated from transition -state theory was the same as the experimental A
factor. Absolute activation energies for reaction (2) have also been obtained
by assuming the activation energies for the higher of the alkanes investigated
were zero.
Bromine hydrogen abstraction reactions analogous to (2) have been
investigated by a similar method. Absolute A factors and activation energies
have been derived by relating the results to the previously found parameters for
bromine atom hydrogen abstraction from methyl bromide.
Previous work, both quantitative and qualitative, of bromine and fluorine
atom hydrogen abstraction and related reactions has been described and the kinetic
data summarised. The activation energies and A factors obtained here for bromine
and fluorine atoms have been compared with previously found figures for chlorine.
Good agreement has been found between experimental A factors and values calculated
from transition -state theory.
From the bromine work carbon -hydrogen bond strengths have been derived
which compare well with the generally accepted values. In order to obtain more
accurate values a method has been developed for obtaining the activation energies
of reactions of the type,
R• + HBr —» RH + Br•
Preliminary results are reported. Arrhenius parameters for other reactions in
the bromine hydrocarbon systems have been considered. Future work has been
suggested.