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Competing rearrangements of ammonium ylides: a quantum theoretical study

Citation

Heard, GL and Yates, BF, Competing rearrangements of ammonium ylides: a quantum theoretical study, Journal of Organic Chemistry, 61, (21) pp. 7276-7284. ISSN 0022-3263 (1996) [Refereed Article]

DOI: doi:10.1021/jo952227w

Abstract

The competition between the Stevens [1,2] and Sommelet-Hauser [2,3] rearrangements for a prototype ylide, N-methyl-3-propenylammonium methylide, has been investigated using ab initio and semiempirical molecular orbital methods. The activation energies for the two processes are remarkably close, separated by only 2 kJ mol -1 at ROMP/6-311+G(d,p). Increasing the size of the basis set leads to a relative stabilization of the Sommelet-Hauser transition geometry, while higher levels of electron correlation (such as CCSD(T)) favor the Stevens rearrangement. Incorporation of solvent effects via the SCRF polarizable continuum model leads to a lowering of the energy barrier of the concerted [2,3] rearrangement, but has little effect on the dissociative [1,2] pathway. The activation energies of both pathways have been calculated for ylides bearing substituents on the ammonium nitrogen and the double bond. Substituents at nitrogen lead to an ylide which is sterically unstable and hence a preference for the dissociative [1,2] rearrangement. Electron-withdrawing substituents on the double bond show a preference for the [2,3] rearrangement, while mildly electron-donating alkyl substituents have very little effect on activation energies.

Item Details

Item Type:Refereed Article
Research Division:Chemical Sciences
Research Group:Physical Chemistry (incl. Structural)
Research Field:Catalysis and Mechanisms of Reactions
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Chemical Sciences
Author:Heard, GL (Mr George Lance Heard)
Author:Yates, BF (Professor Brian Yates)
ID Code:8648
Year Published:1996
Web of Science® Times Cited:11
Deposited By:Chemistry
Deposited On:1996-08-01
Last Modified:2011-08-19
Downloads:0

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