Topological aspects of chemical reactivity. On the possible use of similarity index in characterizing the transition state structure in concerted pericyclic reactions

1987 ◽  
Vol 52 (6) ◽  
pp. 1375-1385
Author(s):  
Robert Ponec
Keyword(s):  
Transition State ◽  
Chemical Reactivity ◽  
Transition States ◽  
Similarity Index ◽  
Pericyclic Reactions ◽  
State Structure ◽  
Transition State Structure ◽  
Topological Similarity

The use of the topological similarity index as a simple means for classification and characterization of the structure of the transition states in concerted pericyclic reactions is discussed. The suggested formulation makes it possible to bring a quantitative aspects into the empirical Dewar's classification of transition states in terms of aromaticity and/or antiaromaticity.

Solvent effects on the structure of SN2 transition states

1978 ◽  
Vol 56 (20) ◽  
pp. 2691-2699 ◽  
Author(s):  
Kenneth Charles Westaway
Keyword(s):  
Transition State ◽  
Isotope Effect ◽  
Solvent Effects ◽  
Kinetic Isotope Effect ◽  
Transition States ◽  
State Structure ◽  
Transition State Structure ◽  
Kinetic Isotope ◽  
Wide Range ◽  
Leaving Group

Two research groups have used heavy atom leaving group kinetic isotope effects to determine how the structure of an SN2 transition state is affected by a change in solvent. Two completely different types of behaviour were observed in these studies. In one case, the leaving group kinetic isotope effect, and thus the transition state structure, changed markedly when the solvent was varied over a reasonably narrow range. In the other study, the leaving group kinetic isotope effect (transition state structure) remained constant over a wide range of solvents. A model describing the interaction between solvent molecules and SN2 transition states is developed and a SolvationruleforSN2reactions which rationalizes the different experimental results is explained and justified. Finally, predictions based on the solvation rule are shown to be in agreement with the results of theoretical calculations of solvent effects on SN2 transition states and secondary α deuterium kinetic isotope effect measurements.

Topological Aspects of Chemical Reactivity. Electron Correlation in the Course of Chemical Reactions

1993 ◽  
Vol 58 (8) ◽  
pp. 1751-1760 ◽  
Author(s):  
Robert Ponec ◽  
Martin Strnad
Keyword(s):  
Chemical Reactions ◽  
Electron Correlation ◽  
Energy Barrier ◽  
Chemical Reactivity ◽  
Similarity Index ◽  
Pericyclic Reactions ◽  
Correlation Effects ◽  
Transient Species

The second order similarity index gRP, which has been proposed recently as a new means for a qualitative characterization of correlation effects in chemical reactivity, was generalized by incorporation into a topological model of the overlap determinant method. The resulting approach, which provides information about the variation of electron correlation during chemical reactions, was applied to the investigation of several selected pericyclic reactions. Consistent with what can be expected, the role of electron correlation was found to be the most critical for transition states of other transient species near the top of the energy barrier. The systematic differences in the extent of electron correlation between allowed and forbidden reactions are also discussed.

Topological aspects of chemical reactivity. On the similarity of molecular structures

1987 ◽  
Vol 52 (3) ◽  
pp. 555-562 ◽  
Author(s):  
Robert Ponec
Keyword(s):  
Electron Density ◽  
Chemical Reactions ◽  
Chemical Reactivity ◽  
Similarity Index ◽  
Molecular Structures ◽  
Similarity Criteria ◽  
Topological Similarity

A topological similarity index is introduced, allowing to characterize quantitatively the extent of reorganization of electron density in the course of chemical reactions. The possible application of this new index for the description and the classification of chemical reactions is discussed on the basis of certain analogy of similarity criteria with the so-called least-motion principle.

Rearrangement of chorismate to prephenate. Use of chorismate mutase inhibitors to define the transition state structure

Biochemistry ◽  
1977 ◽  
Vol 16 (22) ◽  
pp. 4848-4852 ◽  
Author(s):  
P. R. Andrews ◽  
E. N. Cain ◽  
E. Rizzardo ◽  
G. D. Smith
Keyword(s):  
Transition State ◽  
Chorismate Mutase ◽  
State Structure ◽  
Transition State Structure
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