According to the BOLS-NEP notion, atomic undercoordination shortens the Z-X P distance and induces the X P dipole pointing to R. The combination of X P :R attraction and X P ⇔Y repulsion stretches and weakens the R-Y dipole. The degree of atomic undercoordination determines the extent of Z-X P contraction, X P polarization, the stretching force on R-Y, and hence the efficiency of undercoordinated dipolar catalysis .