Surface potential reaction

Pople J A, Krishnan R, Schlegel H B and Binkley J S 1978 Electron correlation theories and their application to the study of simple reaction potential surfaces int. J. Quantum Chem. 14 545-60... 

Transition stale search algorithms rather climb up the potential energy surface, unlike geometry optimi/.ation routines where an energy minimum is searched for. The characterization of even a simple reaction potential surface may result in location of more than one transition structure, and is likely to require many more individual calculations than are necessary to obtain et nilibrinm geometries for either reactant or product. 

The elucidation of the X-ray structure of chymotrypsin (Ref. 1) and in a later stage of subtilisin (Ref. 2) revealed an active site with three crucial groups (Fig. 7.1)-the active serine, a neighboring histidine, and a buried aspartic acid. These three residues are frequently called the catalytic triad, and are designated here as Aspc Hisc Serc (where c indicates a catalytic residue). The identification of the location of the active-site groups and intense biochemical studies led to several mechanistic proposals for the action of serine proteases (see, for example, Refs. 1 and 2). However, it appears that without some way of translating the structural information to reaction-potential surfaces it is hard to discriminate between different alternative mechanisms. Thus it is instructive to use the procedure introduced in previous chapters and to examine the feasibility of different... 

The entropic hypothesis seems at first sight to gain strong support from experiments with model compounds of the type listed in Table 9.1. These compounds show a huge rate acceleration when the number of degrees of freedom (i.e., rotation around different bonds) is restricted. Such model compounds have been used repeatedly in attempts to estimate entropic effects in enzyme catalysis. Unfortunately, the information from the available model compounds is not directly transferable to the relevant enzymatic reaction since the observed changes in rate constant reflect interrelated factors (e.g., strain and entropy), which cannot be separated in a unique way by simple experiments. Apparently, model compounds do provide very useful means for verification and calibration of reaction-potential surfaces... 

Hydrogen abstraction reactions potential surfaces for, 25-26,26,41 resonance structures for, 24 Hydrogen atom, 2 Hydrogen bonds, 169,184 Hydrogen fluoride, 19-20, 20,22-23 Hydrogen molecules, 15-18 energy of, 11,16,17 Hamiltonian for, 4,15-16 induced dipoles, 75,125 lithium ion effect on, 12... 

Bernardi F, Olivucci M, Robb MA (1990) Predicting forbidden and allowed cycloaddition reactions potential surface topology and its rationalization. Acc Chem Res 23 405... 

The reaction between ammonia and methyl halides has been studied by using ab initio quantum-chemical methods.90 An examination of the stationary points in the reaction potential surface leads to a possible new interpretation of the detailed mechanism of this reaction in different media, hr the gas phase, the product is predicted to be a strongly hydrogen-bonded complex of alkylammonium and halide ions, in contrast to the observed formation of the free ions from reaction hr a polar solvent. Another research group has also studied the reaction between ammonia and methyl chloride.91 A quantitative analysis was made of the changes induced on the potential-energy surface by solvation and static uniform electric fields, with the help of different indexes. The indexes reveal that external perturbations yield transition states which are both electronically and structurally advanced as compared to the transition state in the gas phase. 

Electron Correlation Theories and Their Application to the Study of Simple Reaction Potential Surfaces. 

F. Bemardi, M. Olivucci, M. A. Robb, Predicting Forbidden and Allowed Cycloaddition Reactions Potential Surface Topology and Its Rationalization, Acc. Chem. Res. 1990, 23, 405. 

Essentially, the problem falls into two parts. Firstly, the calculation of the multi-body reaction potential surface and secondly, the determination of the properties of the reaction products from the knowledge of the potential surface. The reverse process of inverting experimental data to yield a potential energy surface is more complicated and has rarely been attempted. The calculation of potential surfaces and of product distributions may be carried out at various levels of sophistication using classical, semi-classical or full quantum mechanical treatments. Gross features of the reaction potential surfaces may be related to various product properties by simplistic model calculations. Statistical theories may also be used in cases where the lifetime of the collision is long enough to justify their use. 

J. A. Pople, R. Krishnan, H. B. Schlegel, and J. S. Binkley, hit. J. Quantum Chem., 14, 545 (1978). Electron Correlation Theories and Their Application to the Study of Simple Reaction Potential Surfaces. 

Forbidden and Allowed Cycloaddition Reactions Potential Surface Topology and its Rationalization. 

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