Ab initio molecular orbital studies on a series of pyramidal B3H6X structures (X = NH+, N, CH, BH-, P, PH+, SiH, NO, PO, Co(CO)3) indicate that, for structures where X = NH+, N, and NO, the terminal hydrogens (H(t)) of the basal B3H6 ring are toward the direction of the capping group. In contrast, the H(t)’s are found to be away from the capping group for X = CH, BH-, P, PH+, SiH, PO, and Co(CO)3. All structures except that of B4H7- are calculated to be minima. The six pi interstitial electron rule for three-dimensional delocalization and the compatibility of orbitals in overlap are used to explain the structural and bonding preferences in these pyramidal molecules.