Substituent effects on the molecular and electronic structure of β-lactams

Calculations have been made of the molecular geometry and electron distribution for each of eight unfused β-lactams and thirteen fused β-Iactams, using MINDO/3: electron distributions for unfused β-lactams have been determined by ab initio calculations. Systematic variations with substituent are found in d(C-N) and d(C-O), and in the net atomic charges. The geometrical and electronic effects of imposed non-planarity at nitrogen have been investigated for the parent β-Iactam, azetidin-2-one.