SMALL AND MEDIUM-SIZED BRIDGEHEAD BICYCLIC LACTAMS - A SYSTEMATIC AB-INITIO MOLECULAR-ORBITAL STUDY

Optimized ab initio molecular orbital calculations on nine bridgehead bicyclic lactams ranging from the 2.2.2 to the 4.3.3 series indicate v ariations in structural properties, resonance energies, proton affinit ies, and core orbital ionization energies that reflect the trans-cyclo alkene analogy. The smaller lactams are calculated to be N-protonated, the larger O-protonated, and the ''crossover'' is predicted to occur around the 3.3.1 system. On the basis of resonance energies, larger br idgehead bicyclic lactams could be considered to be hyperstable as Sch leyer and co-workers define the concept for larger bridgehead alkenes. This, hyperstability should be apparent in the kinetics of the nucleo philic substitution reactions of the lactams, such as hydrolysis, but not in the thermochemistry of these reactions.