Correlation of carbon‐13 substituent‐induced chemical shifts revisited: Meta‐ and para‐substituted benzonitriles

Carbon‐13 NMR spectra are reported for 63 substituted benzonitriles in deuteriochloroform or in its mixture with dimethyl sulphoxide‐d6. The substituent‐induced chemical shifts (SCS) of the CN carbon correlate well with dual substituent parameters (DSP) in the para series but poorly in the meta series, whichever parameters are used. The DSP treatment was found to be inferior to principal component analysis (PCA), using as a probe 29 sets of literature data on α,β‐unsaturated benzene derivatives. Whereas one component is sufficient for meta derivatives, two terms are needed for para derivatives, which are different for the α‐ and β‐positions. The constants derived by PCA could be in principle used to predict further SCS, but their scope must be still explored.