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Modern valence-bond description of chemical reaction mechanisms: the 1,3-dipolar addition of diazomethane to ethene

Blavins, J.B., Karadakov, P.B. and Cooper, D.L. (2001) Modern valence-bond description of chemical reaction mechanisms: the 1,3-dipolar addition of diazomethane to ethene. Journal of Organic Chemistry, 66 (12). pp. 4285-4292. ISSN 0022-3263

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Abstract

The electronic mechanism for the gas-phase concerted 1,3-dipolar cycloaddition of diazomethane (CH2N2) to ethene (C2H4) is described through spin-coupled (SC) calculations at a sequence of geometries along the intrinsic reaction coordinate obtained at the MP2/6-31G(d) level of theory. It is shown that the bonding rearrangements occurring during the course of this reaction follow a heterolytic pattern, characterized by the movement of three well-identifiable orbital pairs, which are initially responsible for the π bond in ethene and the C−N π bond and one of the N−N π bonds in diazomethane and are retained throughout the entire reaction path from reactants to product. Taken together with our previous SC study of the electronic mechanism of the 1,3-dipolar cycloaddition of fulminic acid (HCNO) to ethyne (C2H2) (Theor. Chim. Acc. 1998, 100, 222), the results of the present work suggest strongly that most gas-phase concerted 1,3-dipolar cycloaddition reactions can be expected to follow a heterolytic mechanism of this type, which does not involve an aromatic transition state. The more conventional aspects of the gas-phase concerted 1,3-dipolar cycloaddition of diazomethane to ethene, including optimized transition structure geometry, electronic activation energy, activation barrier corrected for zero-point energies, standard enthalpy, entropy and Gibbs free energy of activation, have been calculated at the HF/6-31G(d), B3LYP/6-31G(d), MP2/6-31G(d), MP2/6-31G(d,p), QCISD/6-31G(d) and CCD/6-31G(d) levels of theory. We also report the CCD/6-311++G(2d, 2p)//CCD/6-31G(d), MP4(SDTQ)/6-311++G(2d,2p)//CCD/6-31G(d) and CCSD(T)/6-311++G(2d, 2p)//CCD/6-31G(d) electronic activation energies.

Item Type: Article
Academic Units: The University of York > Chemistry (York)
Depositing User: York RAE Import
Date Deposited: 17 Apr 2009 13:14
Last Modified: 17 Apr 2009 13:14
Published Version: http://dx.doi.org/10.1021/jo015560a
Status: Published
Publisher: American Chemical Society
Identification Number: 10.1021/jo015560a
URI: http://eprints.whiterose.ac.uk/id/eprint/6799

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