A. Greenberg et Ca. Venanzi, STRUCTURES AND ENERGETICS OF 2 BRIDGEHEAD LACTAMS AND THEIR N-PROTONATED AND O-PROTONATED FORMS - AN AB-INITIO MOLECULAR-ORBITAL STUDY, Journal of the American Chemical Society, 115(15), 1993, pp. 6951-6957
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.