Computational methods for conformational analysis of unsymmetrical 1,3-diamines: 3-aminotropanes

A comparative study has been performed to evaluate the ability of a range o f computational theories to predict the relative basicity and the conformat ions of diamine systems. Specifically, molecular mechanics (MM3), semiempir ical (AM1), and ab initio (Hartree-Fock) methods have been used in the conf ormational analyses of unprotonated, monoprotonated, and diprotonated 3-ami notropanes, a pair of isomeric 1,3-diamines. Use of the molecular mechanics force field, with the recently determined parameter set for protonated ami nes, affords results that are in agreement with experimental data, when cor rected for water solvent (by setting the dielectric constant to 80). Ab ini tio and semiempirical calculations, in contrast, give inconsistent and inco rrect results. (C) 1999 John Wiley & Sons, Inc.