Face selectivity for the reactions of 5-substituted (X)-2-dicyanomethyleneadamantanes with a Grignard reagent was examined using ab initio calculation for the substituents (X=F, Cl, Br, OH, NH2, and CH 3 ). The calculated syn/anti product ratio based on the results of transition state energies for the halide substituents are in good agreement with the available experimental results. In addition, the results of the natural bond orbital calculation suggest that the through-bond Cieplak hyperconjugation effect, instead of the through-space interaction suggested by the experimental results in a prior study, is the main factor in determining face selectivity for the halide substituents in the present study, while for (X=OH, NH2, and CH3) substituents, other interactions may have unnegligible effects as well.