The 13C nuclear magnetic resonance substituent chemical shifts of 2-substituted indenes. Interpretation by a multivariate data analysis method

Abstract

The ¹³C n.m.r. chemical shifts of several 2-substituted indenes are reported and the induced substituent shieldings of the remote proton-bearing aromatic carbons are analysed by a multivariate data analysis method. A dual parameter model is necessary to describe the shift variations and the two components obtained were found to correlate to a mesomeric σ_R° and field–inductive σ_I scale, respectively. The two dual parameter models are tested on a structurally similar heterocyclic system. The limitations of multiparameter equations in predicting ¹³C chemical shifts and in separating electronic effects are briefly discussed.