Effect of Electronegative Substituents and Angular Dependence on the Heteronuclear Spin−Spin Coupling Constant 3JC−H: An Empirical Prediction Equation Derived
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- 作者：Giulia Palermo ; Raffaele Riccio ; Giuseppe Bifulco
- 刊名：Journal of Organic Chemistry
- 出版年：2010
- 出版时间：March 19, 2010
- 年：2010
- 卷：75
- 期：6
- 页码：1982-1991
- 全文大小：953K
- 年卷期：v.75,no.6(March 19, 2010)
- ISSN：1520-6904
文摘
A general carbon−proton vicinal coupling constant (3JC−H) prediction equation has been empirically derived by a coupling constant database of 2157 3JC−H calculations (at the hybrid DFT MPW1PW91/6-31G(d,p) level). The equation includes the electronegativity effect of the substituents attached to the 13C−C−C−1H fragment and the dihedral (Φ) dependence of the heteronuclear spin-coupling. A set of butane and pentane models were built, systematically varying both the Φ torsion angle in 30° steps and the substitution pattern with several electronegative substituents (Br, NH2, F, Cl, SH, OH) in order to obtain the coupling constant database. The here reported 3JC−H equation is a quantitative prediction tool, particularly useful as a support in the analysis of NMR data for the structural elucidation of organic compounds characterized by specific substitution patterns. To confirm the accuracy of our equation in the prediction of the experimental 3JC−H couplings, we tested the equation, comparing 114 experimental 3JC−H values obtained from 29 polysubstituded benchmark organic compounds with the predicted data. In addition, a set of 3JC−H coupling bidimensional Karplus-type curves correlating the calculated 3JC−H values to the specific dihedral angle for every substitution pattern considered were built in order to evaluate the magnitude of the electronegativity effect.