  This work reports a theoretical study of the gas phase unimolecular
decomposition of cyclobutane, cyclopentane and cyclohexane by means of quantum
chemical calculations. A biradical mechanism has been envisaged for each
cycloalkane, and the main routes for the decomposition of the biradicals formed
have been investigated at the CBS-QB3 level of theory. Thermochemical data
(?H\degree f, S\degree, C\degree p) for all the involved species have been
obtained by means of isodesmic reactions. Rate constants have been derived for
all elementary reactions using transition state theory at 1 atm and
temperatures ranging from 600 to 2000 K. These values have been compared with
the few data available in the literature and showed a rather good agreement.
