Through-bond and through-space interactions between lone pairs in bicyclic diamines and related compounds

Through-bond and through-space interactions between nitrogen lone pairs are studied using ab initio methods for a series of symmetric bicyclic diamines with up to four -CH 2 - units in each bridge and for the molecules obtained by removing one and two of the methylene bridges. In all cases there are contributions to the odd-even splitting Δ=E(n - )-E(n + ) from through-space as well as through-bond interactions with a tendency for cancellation. The dependence of |Δ| on the number of bonds of the bridge is nonexponential at least for short bridges