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 of computational theories to predict the relative basicity and the Ž . conformations of diamine systems. Specifically, molecular mechanics MM3 , Ž . Ž . semiempirical AM1 , and ab initio Hartree]Fock methods have been used in the conformational analyses of unprotonated, monoprotonated, and diprotonated 3-aminotropanes, a pair of isomeric 1,3-diamines. Use of the molecular mechanics force field, with the recently determined parameter set for protonated amines, affords results that are in agreement with experimental data, when corrected for Ž . water solvent by setting the dielectric constant to 80 . Ab initio and semiempirical calculations, in contrast, give inconsistent and incorrect results. Q 1999 John Wiley & Sons, Inc. J Comput Chem 20: 1371]1378, 1999