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A computational study of the 1,3-dipolar cycloaddition reaction mechanism for nitrilimines

Title:

A computational study of the 1,3-dipolar cycloaddition reaction mechanism for nitrilimines

Mawhinney, Robert C. and Muchall, Heidi M. and Peslherbe, Gilles H. (2005) A computational study of the 1,3-dipolar cycloaddition reaction mechanism for nitrilimines. Canadian Journal of Chemistry, 83 (9). pp. 1615-1625. ISSN 0008-4042

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Official URL: http://dx.doi.org/10.1139/v05-179

Abstract

The [3+2] and [1+2] cycloaddition pathways between ethene and a series of 13 nitrilimines (R1CNNR2) have been examined by density functional theory [PBE0/6-311++G(2df,pd)] calculations. All reactions have low barriers ranging from 14.14 (R1 = CH3, R2 = H) to 1.01 (R1 = R2 = F) kcal mol–1, and large reaction exothermicities consistent with the transient nature of nitrilimines. The [3+2] and [1+2] transition-state structures are very similar, mainly differing in the relative orientation of their fragments and the newly forming C—C bond distance, and exhibit only minor deviations from the structures of the reactants. Both reaction pathways are concerted and asynchronous, but the [1+2] reaction has a greater degree of asynchronicity. Examination of the frontier molecular orbitals reveals that both the [3+2] and [1+2] barrier heights are related to two sets of orbital interactions, with the interaction between the lowest unoccupied molecular orbital π of nitrilimine and the highest occupied molecular orbital of ethene in common. The second interaction in both cases is carbene-like. A relationship between the weights of the 1,3-dipolar resonance contribution in the various nitrilimines and the corresponding [3+2] barrier heights was not found, but a good correlation could be found between the [1+2] barrier heights and both the 1,3-dipolar and carbene contributions. Inspection of the potential energy surface in the vicinity of the two transition states for the reaction between unsubstituted nitrilimine and ethene suggests that the observed [3+2] product is a result of an initial carbene-like approach of the two fragments followed by a ridge bifurcation that leads to the [3+2] product minimum.

Divisions:Concordia University > Faculty of Arts and Science > Chemistry and Biochemistry
Item Type:Article
Refereed:Yes
Authors:Mawhinney, Robert C. and Muchall, Heidi M. and Peslherbe, Gilles H.
Journal or Publication:Canadian Journal of Chemistry
Date:September 2005
Funders:
  • Fonds Québecois de Recherche sur la Nature et les Technologies
Keywords:nitrilimines, 1,3-dipole, carbene, [3+2] cycloaddition, [1+2] cycloaddition, density functional theory (DFT)
ID Code:6763
Deposited By:DANIELLE DENNIE
Deposited On:12 Jul 2010 16:39
Last Modified:08 Dec 2010 18:10
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