STRUCTURES AND ENERGETICS OF 2 BRIDGEHEAD LACTAMS AND THEIR N-PROTONATED AND O-PROTONATED FORMS - AN AB-INITIO MOLECULAR-ORBITAL STUDY

Ab initio molecular orbital calculations optimized with the 6-31G bas is set were employed to investigate the structures, resonance energies , and protonation sites of the two bridgehead bicyclic lactams 1-azabi cyclo[2.2.2]-octan-2-one (2-quinuclidone) and 1-azabicyclo[3.3.1]nonan -2-one. The structures and resonance energies reflect the absence of r esonance stabilization in the first molecule and somewhat reduced reso nance in the second molecule. While planar amides protonate on oxygen, 2-quinuclidone very strongly favors N-protonation while the N- and O- protonated forms in the 3.3.1 system are almost equal in energy. Discu ssion of structures and energies is given in the context of resonance theory.