Substituent effect study on13CβSCS of styrene series. A Yukawa-Tsuno model and Reynolds dual substituent parameter model investigation
| Autor: | Sabih A. Al-Shawi, Basil A. Saleh, Ghazwan F. Fadhil |
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| Rok vydání: | 2008 |
| Předmět: | |
| Zdroj: | Journal of Physical Organic Chemistry. 21:96-101 |
| ISSN: | 1099-1395 0894-3230 |
| DOI: | 10.1002/poc.1272 |
| Popis: | The Yukawa–Tsuno (Y–T) and Reynolds dual substituent parameter (DSP) models have been used to model 13C substituent chemical shift (SCS) of the Cβ atom of 19 series of para-substituted styrenes (X-C6H4CRCYW) with variable electronic and structural demands in the side-chain. The best fit of the Y–T model was better than that of the Reynolds DSP model for most of the studied series. A high correlation was found between the ρ value of the Y–T model and ρF value of the Reynolds DSP model. The ρ value, which reflects the sensitivity of 13Cβ SCS to the substituent field effect, was found to be influenced by the group W on the Cβ atom. A W group that enhances the para-substituent π-polarization of the side-chain has a higher ρ value than its counterpart W groups that induce counter π-polarization in the side-chain. The series with W in an E-configuration to the aryl ring has higher ρ value than corresponding Z series. A lower ρ value is observed when W induces a counter π-polarization of the side-chain (as with NO2 and COMe) or when the R substituent imposes a 65° dihedral angle between the side-chain and the para-substituted benzene ring (as with t-Bu). When the W group is a heterocyclic ring, the closer the heteroatom is to Cβ, the lower the ρ value is due to the greater counter π-polarization. The two components of the substituent effect on 13Cβ SCS, namely the field effect and resonance effect, behave inversely. The resonance demand (r+ value) increases, as the Y and/or W groups become more electron-withdrawing (EW). The series with W as a hetrocyclic ring develop negative charge at the carbon atom of the hetrocyclic ring adjacent to Cβ (and to which the styryl moiety is attached) and has a lower r+ value than those which fail to do so. The lowest r+ value was for those series with a 65° dihedral angle. Copyright © 2007 John Wiley & Sons, Ltd. |
| Databáze: | OpenAIRE |
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