The AMI semiempirical method has been used to calculate the heats of formation and preferred conformations of a variety of dioxolanes and related compounds, and of the radicals derived from them. The heats of formation and conformations of the transition structures for hydrogen-atom transfer from trialkylstannane to some of these radicals have also been determined. Among the major conclusions of this study are the following : the results of the calculations are highly consistent with experimental data; the regiochemistry of hydrogen-atom abstraction from dioxolanes is controlled mainly by thermochemical factors; the Sn---H---C bond angle in the transition structure for hydrogen-atom transfer is close to 180 degrees; the calculated activation energies for reactions of dioxolanonyl radicals with trialkylstannane agree with observed diastereoselectivities; and the bond lengths and charge distribution in radicals bearing an a-ether and an alpha-carbonyl substituent are consistent with captodative stabilization.