Carbon‐13 nuclear magnetic resonance spectroscopy—VII:para‐substituted fluorobenzenes

Abstract

C‐13 and F‐19 NMR spectra of seventeen para‐substituted fluorobenzenes were measured and the chemical shifts as well as coupling constants with respect to substituents were analysed. The chemical shifts of the fluorine, the C₁ and the C₂ atoms were found to depend on the total electron densities. In the case of the C₃ atom, the chemical shifts seem to depend on π‐electron densities rather than the total electron densities. The present calculations also indicate that the chemical shift of the C₄ atom depends mainly on σ‐electron densities due to the inductive effects of substituents. The strongest factor influencing the coupling constant, ⁿJ(CF), is also considered to be the π‐electron densities on the carbon atoms. In the case of the direct couplings, ¹J(CF), the π‐bond orders are important.