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

• Main Authors: Valentić Nataša V., Vitnik Željko J., Kozhushkov Sergei I., de Majere Armin, Ušćumlić Gordana S., Juranić Ivan O.
• Format: Article
• Language: English
• Published: Serbian Chemical Society 2003-01-01
• Series: Journal of the Serbian Chemical Society
• Subjects: [3]dendralenes; unsaturated chain carbon 13c scs; substituent effects; reverse 13c scs effect; mndo-pm3 calculations
• Online Access: http://www.doiserbia.nb.rs/img/doi/0352-5139/2003/0352-51390302067V.pdf
• ISSN: 0352-5139; 1820-7421

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 ¶-system in the unsaturated chain (¶-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.