13C and 19F NMR Spectra of substituted ethyl α-fluorocinnamates. Application of the DSP-NLR equation
1990; Elsevier BV; Volume: 46; Issue: 2 Linguagem: Inglês
10.1016/s0040-4020(01)85418-1
ISSN1464-5416
AutoresCharles N. Robinson, Gregory E. Stablein, Carl Slater,
Tópico(s)Chemical Synthesis and Analysis
Resumo13C and 19F NMR spectra of 12 p-substituted and 9 m-substituted ethyl α-fluorocinnamates, along with that of the parent compound, have been recorded and analyzed by DSP and DSP-NLR equations. ϵ values found for the correlation of chemical shifts of both the β-carbon atom of the styrene skeleton and the F atom show near additivity of the effect of individual substituents on C4 shifts in p-disubstituted benzenes. Despite this, correlations using the DSP-NLR equation are not greatly improved over those of the DSP equation, either for sites showing excellent or poor correlations. Also, the magnitude of the ϵ values appropriate for different sites on the side chain show no significant relationship to the percentage of the sensitivity at the site attributed to resonance interaction. Consequently, the utility of the DSP-NLR method seems limited. Substituent effects at F are normal, in contrast to the expectation based on charge alternation that they would be inverse. CNDO/2 charge densities calculated for representative methyl α-fluorocinnamates reveal that π densities at both F and the β-carbon atom of the styrene skeleton accord with normal substituent effects.
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