Density functional theory and correlated ab initio quantum mechanical methods were used to locate and analyze alkene hydroboration transition structures for 10-R-9-borabicyclo[3.3.2]decane reagents. Transition-state ensembles quantitatively modeled enantioselectivity for hydroboration of cis-, trans-, and gem-disubstituted alkenes in excellent agreement with experiment. The 10-R group and borabicyclo[3.3.2]decane ring conformation effects were analyzed to understand the origin of asymmetric selectivity.