A comparison of the MNDO and AM1 SCF-MO energy surfaces for dipolar cycloaddition and [3,3] sigmatropic reactions

Abstract

Difference contour energy maps for several π4s+π2s dipolar cycloadditions and for the [3,3] sigmatropic (Claisen) rearrangement of pent-4-enal indicate that the AM1 and MNDO SCF-MO methods differ most significantly at C–C, C–O, and C–N bond distances of approximately 2.3, 2.05, and 2.5 Å, respectively; the AM1 results for bond formation involving nitrogen appear to be incorrect owing to excessive core–core repulsion.