Development of Practical MO Techniques for the Prediction of the Properties and Behavior of Materials.
Abstract
A third generation semiempirical SCF MO treatment (AM1) has been developed in which the weaknesses of MNDO, in particular failure to reproduce hydrogen bonds, have been overcome. MNDO has been parameterized for Zn, Hg, Ge, Sn, Pb, Br, and I and reparametrized for Si and S. A version of MNDO with d AOs has been parametrized for chromium. Our computer programs have been improved and collected into a single package (MOPAC) which allows calculations of a wide variety of molecular properties, and additional graphics packages developed. Extensive calculations for pericyclic reactions has led to a new general rule, that multibond processes are not normally synchronous. The Diels-Alder reactions in particular have been shown to involve unsymmetrical transition states. Studies of aniotic nucleophilic substitution have shown that the barriers in solution can be due entirely to desolvation of the anion, a result of major theoretical significance. Deriving from (2), a new explanation of the rates and specificities of enzyme reactions. Refutation of FO Theory as an effective general treatment of chemical reactions. A new interpretation of sigma interactions in molecules (sigmaconjugation). Evidence that tunnelling can play a more general role in chemistry than previously thought.
Document Details
- Document Type
- Technical Report
- Publication Date
- Oct 08, 1985
- Accession Number
- ADA161992
Entities
People
- Michael J. S. Dewar
Organizations
- University of Texas at Austin