Force field methods conjugated systems

General Systems.—Allinger et al. have applied the force-field method to calculations of the energy and conformation of cyclic non-conjugated olefins, including cycloheptene, isomeric cyclo-octeries, cyclo-octadienes, and cyclo-decenes, and cis,cis-cyclodeca-l,6-diene the latter is predicted to exist as a 65 35 chair-boat mixture. Similar calculations have been carried out for various cyclic ketones. Cycloheptanone is expected to exist as a mixture of conformers, whereas cyclo-octanone and cyclononanone should exist as (1) and (2), respectively. The conformation (3 X = Hj) predicted for cyclo-... 

An alternative approach to the finite element approach is one, introduced as a concept by Courant as early as 1943 [197], in which the total energy functional, implicit in the finite element method, is directly minimized with respect to all nodal positions. The approach is conjugate to the finite element method and merely differs in its procedural approach. It parallels, however, methods often used in atomistic modeling schemes where the potential energy functional of a system (e. g., given by the force field ) is minimized with respect to the position of all (or at least many) atoms of the system. A simple example of this emerging technique is given below. 

Hybrid potentials of the type discussed in this chapter have been in use for twenty five years or so. Some of the earliest examples were those designed to study conjugated organic molecules in which the -electrons of the system were treated with a semiempirical QM method and the cr-bonding framework was described with a MM force field [8, 9], The methods were used to study the structure and spectra of the molecules [10, 11] and photoisomerization processes [12, 13], The first true combined potential in which both a and w electrons were considered in the quantum mechanical region was also developed by Warshel, in collaboration with Levitt, which they used to study the mechanism of the enzyme, lysozyme [14], They combined a semiempirical QM method to describe a portion of the enzyme and the substrate, and a standard MM force field to describe the rest of the atoms. 

Carbocation Stabilities Comparison of Theory and Experiment Force Fields A General Discussion Mixed Quantum-Classical Methods Molecular Mechanics Conjugated Systems. 

Divide and Conquer for Semiempirical MO Methods Force Fields A Brief Introduction Force Fields A General Discussion Hyperconjugation MNDO Molecular Mechanics Conjugated Systems Monte Carlo Quantum Methods for Electronic Structure PM3 PRDDO SINDOl Parameterization and Application. 

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