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Title: Evaluation of the Kinetic Data for Intramolecular 1, x-Hydrogen Shifts in Alkyl Radicals and Structure/Reactivity Predictions from the Carbocyclic Model for the Transition State

Abstract

Experimental and computational kinetic data for the intramolecular 1,x-hydrogen shift in alkyl radicals are compiled in Arrhenius format for x = 2-5. Significant experimental disparity remains, especially for x = 2 and 3. Experimental data for radicals with tert centers or bearing spectator substituents are lacking for all x, and none exist for x = 6. The common use of the strain energy of the unsubstituted (x+1)-carbocycle to coarsely model the activation energy for the 1,x-shift is extended to explore more subtle differences in progressively methyl-substituted systems by use of molecular mechanics estimates of differences in strain between radicals and carbocycles. For x = 5 and 6, a sterically driven increase in E is predicted for shifts in the tert {yields} tert class that apparently runs counter to the behavior of bimolecular hydrogen transfers. In contrast, a sterically driven decrease in E is predicted to result from spectator methyl groups for the prim {yields} prim reaction class for all x. There is no experimental basis to test these predictions; fragmentary computational evidence lends some support to the second but is ambiguous concerning the first. Possible deficiencies in the use of carbocycles as transition state models are discussed.

Authors:
 [1]
  1. ORNL
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
931275
DOE Contract Number:  
DE-AC05-00OR22725
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Organic Chemistry; Journal Volume: 72; Journal Issue: 1
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ACTIVATION ENERGY; ALKYL RADICALS; HYDROGEN TRANSFER; CHEMICAL REACTION KINETICS; KINETIC EQUATIONS

Citation Formats

Poutsma, Marvin L. Evaluation of the Kinetic Data for Intramolecular 1, x-Hydrogen Shifts in Alkyl Radicals and Structure/Reactivity Predictions from the Carbocyclic Model for the Transition State. United States: N. p., 2006. Web.
Poutsma, Marvin L. Evaluation of the Kinetic Data for Intramolecular 1, x-Hydrogen Shifts in Alkyl Radicals and Structure/Reactivity Predictions from the Carbocyclic Model for the Transition State. United States.
Poutsma, Marvin L. Sun . "Evaluation of the Kinetic Data for Intramolecular 1, x-Hydrogen Shifts in Alkyl Radicals and Structure/Reactivity Predictions from the Carbocyclic Model for the Transition State". United States. doi:.
@article{osti_931275,
title = {Evaluation of the Kinetic Data for Intramolecular 1, x-Hydrogen Shifts in Alkyl Radicals and Structure/Reactivity Predictions from the Carbocyclic Model for the Transition State},
author = {Poutsma, Marvin L},
abstractNote = {Experimental and computational kinetic data for the intramolecular 1,x-hydrogen shift in alkyl radicals are compiled in Arrhenius format for x = 2-5. Significant experimental disparity remains, especially for x = 2 and 3. Experimental data for radicals with tert centers or bearing spectator substituents are lacking for all x, and none exist for x = 6. The common use of the strain energy of the unsubstituted (x+1)-carbocycle to coarsely model the activation energy for the 1,x-shift is extended to explore more subtle differences in progressively methyl-substituted systems by use of molecular mechanics estimates of differences in strain between radicals and carbocycles. For x = 5 and 6, a sterically driven increase in E is predicted for shifts in the tert {yields} tert class that apparently runs counter to the behavior of bimolecular hydrogen transfers. In contrast, a sterically driven decrease in E is predicted to result from spectator methyl groups for the prim {yields} prim reaction class for all x. There is no experimental basis to test these predictions; fragmentary computational evidence lends some support to the second but is ambiguous concerning the first. Possible deficiencies in the use of carbocycles as transition state models are discussed.},
doi = {},
journal = {Journal of Organic Chemistry},
number = 1,
volume = 72,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2006},
month = {Sun Jan 01 00:00:00 EST 2006}
}