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Journal of Wood Science

Official Journal of the Japan Wood Research Society

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Transition state leading to β-O′ quinonemethide intermediate of p-coumaryl alcohol analyzed by semi-empirical molecular orbital calculation

Journal of Wood Science volume 52, pages 128–133 (2006)Cite this article

Abstract

The radical coupling reaction leading to the β-0′ quinonemethide intermediate of p-coumaryl alcohol was analyzed by semi-empirical molecular orbital calculation with MOPAC2002. By analyzing the radical monomer in a one-electron oxidation, the spin density of the unpaired electron at the 4-oxygen was less than half of the values at the C1, C3, C5, and Cβ positions. By analyzing the transition state during the radical coupling reaction, the activation enthalpy was evaluated as 9.76 kcal/mol, which corresponds to the activation energies for the propagation of common vinyl polymers. From the analysis of atomic interactions in the transition state, it was found that the activation enthalpy was largely composed of a high coulombic repulsion between Cβ of the first monomer and the phenolic oxygen of the second monomer. After passing the transition state, the two radical monomers formed a metastable quinone-methide intermediate. The optimum conformation of the quinonemethide intermediate was formed from the meta-stable conformation through a second transition state with a small energy barrier.

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Authors and Affiliations

  1. Faculty of Applied Biological Sciences, Gifu University, Gifu, 501-1193, Japan

    Mikiji Shigematsu, Takayuki Kobayashi, Hiroyasu Taguchi & Mitsuhiko Tanahashi

Authors
  1. Mikiji Shigematsu
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  2. Takayuki Kobayashi
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  3. Hiroyasu Taguchi
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  4. Mitsuhiko Tanahashi
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Corresponding author

Correspondence to Mikiji Shigematsu.

Additional information

Part of this article was presented at the 46th Lignin Symposium, held in Fukuoka, October 31-November 1, 2002

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Shigematsu, M., Kobayashi, T., Taguchi, H. et al. Transition state leading to β-O′ quinonemethide intermediate of p-coumaryl alcohol analyzed by semi-empirical molecular orbital calculation. J Wood Sci 52, 128–133 (2006). https://doi.org/10.1007/s10086-005-0737-4

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  • DOI: https://doi.org/10.1007/s10086-005-0737-4

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