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Understanding conjugation and hyperconjugation from electronic delocalization measures

The concepts of conjugation and hyperconjugation play an important role to provide an explanation for several fundamental phenomena observed in organic chemistry. Because these effects cannot be directly measured experimentally, their assessment became a primary concern for chemists from the very beginning. In general, the stabilization produced by both phenomena has been studied by means of isodesmic reactions and energy based analysis such as the energy decomposition analysis. In recent years, electronic delocalization measures have been successfully applied to elucidate the nature of chemical bonding and the aromatic character of all kind of molecules. Because conjugation and hyperconjugation stabilizations are strongly linked to the concept of electron delocalization, this paper will give an account of both effects from the point of view of electronic delocalization measures calculated within the framework of the quantum theory of atoms in molecules. In particular, we focus our attention in the controversial case of the stabilization by conjugation in 1,3-butadiyne and 1,3-butadiene. Unexpectedly, theoretical calculations based on the scheme proposed by Kistiakowsky to quantify the extent of stabilization due to conjugation predicted that the conjugation of 1,3-butadiyne was zero. Subsequent energetic analyses contradicted this observation. These studies pointed out the presence of hyperconjugation stabilization in the hydrogenated product of 1,3-butadiyne and 1,3-butadiene that were used as reference systems in the Kistiakowsky’s scheme. Consequently, the extra stabilization of 1-butyne due to hyperconjugation hides the stabilization by conjugation of 1,3-butadiyne. Our results based on electron delocalization measures confirm both the presence of conjugation in 1,3-butadiene and 1,3-butadiyne and hyperconjugation stabilization in their respective hydrogenated products, 1-butene and 1-butyne

Financial help has been furnished by the Spanish MICINN Projects No. CTQ2008-03077/BQU, CTQ2011-23156/BQU and CTQ2008-06532/BQU and by the Catalan DIUE through projects No. 2009SGR637 and 2009SGR528. J.P. thanks the MICINN the Ramon y Cajal contract. Support for the research of M.S. was received through the ICREA Academia 2009 prize for excellence in research funded by the DIUE of the Generalitat de Catalunya

© Journal of Physical Chemistry A, 2011, vol. 115, núm. 45, p. 13104-13113

American Chemical Society (ACS)

Manager: Ministerio de Educación y Ciencia (Espanya)
Ministerio de Ciencia e Innovación (Espanya)
Author: Feixas Geronès, Ferran
Matito i Gras, Eduard
Poater i Teixidor, Jordi
Solà i Puig, Miquel
Date: 2011 November 17
Abstract: The concepts of conjugation and hyperconjugation play an important role to provide an explanation for several fundamental phenomena observed in organic chemistry. Because these effects cannot be directly measured experimentally, their assessment became a primary concern for chemists from the very beginning. In general, the stabilization produced by both phenomena has been studied by means of isodesmic reactions and energy based analysis such as the energy decomposition analysis. In recent years, electronic delocalization measures have been successfully applied to elucidate the nature of chemical bonding and the aromatic character of all kind of molecules. Because conjugation and hyperconjugation stabilizations are strongly linked to the concept of electron delocalization, this paper will give an account of both effects from the point of view of electronic delocalization measures calculated within the framework of the quantum theory of atoms in molecules. In particular, we focus our attention in the controversial case of the stabilization by conjugation in 1,3-butadiyne and 1,3-butadiene. Unexpectedly, theoretical calculations based on the scheme proposed by Kistiakowsky to quantify the extent of stabilization due to conjugation predicted that the conjugation of 1,3-butadiyne was zero. Subsequent energetic analyses contradicted this observation. These studies pointed out the presence of hyperconjugation stabilization in the hydrogenated product of 1,3-butadiyne and 1,3-butadiene that were used as reference systems in the Kistiakowsky’s scheme. Consequently, the extra stabilization of 1-butyne due to hyperconjugation hides the stabilization by conjugation of 1,3-butadiyne. Our results based on electron delocalization measures confirm both the presence of conjugation in 1,3-butadiene and 1,3-butadiyne and hyperconjugation stabilization in their respective hydrogenated products, 1-butene and 1-butyne
Financial help has been furnished by the Spanish MICINN Projects No. CTQ2008-03077/BQU, CTQ2011-23156/BQU and CTQ2008-06532/BQU and by the Catalan DIUE through projects No. 2009SGR637 and 2009SGR528. J.P. thanks the MICINN the Ramon y Cajal contract. Support for the research of M.S. was received through the ICREA Academia 2009 prize for excellence in research funded by the DIUE of the Generalitat de Catalunya
Format: application/pdf
Citation: 015422
ISSN: 1089-5639 (versió paper)
1520-5215 (versió electrònica)
Document access: http://hdl.handle.net/10256/11432
Language: eng
Publisher: American Chemical Society (ACS)
Collection: MEC/PN 2009-2011/CTQ2008-03077/BQU
MICINN/PN 2012-2014/CTQ2011-23156
MEC/PN 2009-2011/CTQ2008-06532/BQU
AGAUR/2009-2014/2009 SGR-637
AGAUR/2009-2014/2009 SGR-528
Reproducció digital del document publicat a: http://dx.doi.org/10.1021/jp205152n
Articles publicats (D-Q)
Is part of: © Journal of Physical Chemistry A, 2011, vol. 115, núm. 45, p. 13104-13113
Rights: Tots els drets reservats
Subject: Compostos orgànics
Organic compounds
Enllaços químics
Chemical bonds
Orbitals moleculars
Molecular orbitals
Title: Understanding conjugation and hyperconjugation from electronic delocalization measures
Type: info:eu-repo/semantics/article
Repository: DUGiDocs

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