Journal of the Serbian Chemical Society (Feb 2003)

Effect of substituents on the 13C-NMR chemical shifts of 3-methylene-4-substituted-1,4-pentadienes. Part I.

  • IVAN O. JURANIC,
  • ARMIN DE MEIJERE,
  • GORDANA S. USCUMLIC,
  • SERGEI I. KOZHUSHKOV,
  • ZELJKO VITNIK,
  • NATASA V. VALENTIC

Journal volume & issue
Vol. 68, no. 2
pp. 67 – 76

Abstract

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The principles of linear free energy relationships were applied to the 13C substituent chemical shifts (SCS) of the carbon atoms in the unsaturated chain of 3-methylene-4-substituted-1,4-pentadienes. Correlations of the SCS with the substituent parameters of Swain and Lupton provide a mutually consistent picture of the electronic effects in these compounds. The pattern of the electronic effects can be fully rationalized by a model based on the direct transmission of substituent effects through-space (direct through-space field effects), and via conjugative interactions (resonance effects), or by substituent-induced polarization of the p-system in the unsaturated chain (p-polarization effect). Semi-empirical MNDO-PM3 calculations suggest the s-cis conformation of 3-methylene-4-substituted-1,4- -pentadienes as the one with minimal heat of formation.

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