Cationic intermediates in trans- to cis- isomerization reactions of allylic systems. An exploratory ab initio study

Jenny C.Y. Yeung, Gregory A. Chasse, Edwin J. Frondozo, Ladislaus L. Torday, Julius G. Papp

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Abstract

Computational analyzes were undertaken to investigate the geometrical isomerization mechanism of a truncated tail-end model (C1-C10) of the full lycopene molecule, the products of which are the 5-cis and 7-cisforms. The global conformational minima were identified for the neutral all-trans reactant, the cationic isomerization intermediates and that of these two cis-isomeric products. Energies and stabilities were compared during different stages of the isomerization mechanism of the segments. The C4 allylic hydride affinity values of the all-trans to the 5-cis, and the 7-cis isomers of this lycopene model, are in the range of 255-260 kcal mol-1, which are within the expected limits of such hydride affinity values (210 kcal mol-1 for weak and 360 kcal mol-1 for strong hydride affinity) at the RHF/3-21G level of theory. The bond lengths involving alternating single and double carbon-carbon bonds roughly coincide with the expected changes along each intermediate of the putative isomerization pathway. The following sequence of stability was observed in the tail-end model of neutral lycopene isomers: 5-cis > all-trans > 7-cis For the cation, the order of stability was different: all-trans > 5-cis > 7-cis

Original languageEnglish
Pages (from-to)143-162
Number of pages20
JournalJournal of Molecular Structure: THEOCHEM
Volume546
Issue number1-3
DOIs
Publication statusPublished - Jul 16 2001

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Keywords

  • 1,4-pentadiene
  • Ab initio molecular orbital computations
  • Antioxidant
  • Carotenoids
  • Lycopene
  • Oxidative stress
  • Tail-end model (C-C) of lycopene
  • Trans- to cis-isomerization

ASJC Scopus subject areas

  • Biochemistry
  • Condensed Matter Physics
  • Physical and Theoretical Chemistry

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