Molecular Simulation of Hydrogen Bonds, Diels-Alder Reactions, Urethane Formation from Isocyanates andPhotochromism of Dithienylethenes byNew MOPAC2016 Hamiltonians and the Evaluation

Abstract

Recently MOPAC2016 hamiltonian was announced to be opened up by improvement of weak bond energies in molecules and their reactions.

We then simulated basic hydrogen bonds, stereoselective Diels-Alder reactions, practical urethane formation from isocyanates and photochromic cyclization/cycloreversion of references [1] by use of the PM7 levels. The calculated molecular structures and some energies were speculated by experimental data and other ab initio level informations. The hydrogen bond structure and energies (E_Hb), interaction energies (E_In), activation energies (E_a) of the two reactions by PM7 and PM7-TS were inferred to be improved from PM6 and similar to MP2/6-31+G (d,p) etc., and to come from by the good balance of small interaction energies such as dispersion energies. The large E_In energies by PM7 and MP2 suggest to check the existence of the intermediate complexes B in the two kinds of reactions by low temperature NMR etc..

The improved and compact MOPAC2016 (PM7 etc.) are very recommended to use in educational and experimental fields.