Free radical-mediated 5-exo-trig cyclizations of hepta-1,6-dienes incorporating allylsilane, alkyl and alkoxy analogues are modeled using correlated ab initio calculations. The structural, electronic and thermochemical properties of reactants, products and transition species involved in the key step of the radical cyclization process are analyzed and compared with those predicted by the Beckwith-Houk transition models. The product ratios are calculated from the Gibbs energy differences between the possible transition structures following the Curtin-Hammet principle and compared to experimental values.