Relative Basicities of Some Endo and Exo Norbornylamines

A series of endo- and exo-norbornylamines were synthesized and their relative basicities determined in acetonitrile and dimethylformamide solvents. The exo isomer is always more basic than the corresponding endo isomer in either solvent. All of the bicyclic amines studied have higher pK(a)'s in acetonitrile solvent than in dimethylformamide except for the 2-morpholinonorbornanes which are just the reverse. This effect is explained by the ability of the morpholine group to disperse a positive charge and the relative polarizabilities of the solvents. Semiempirical AM1 and PM3 methods along with ab initio HF/STO-3G, HF/3-21G, and HF/6-31G methods were used to calculate proton affinities and dipole moments for each of the amines. The results of the theoretical calculations correspond well with the experimental observations.