Application of principal component analysis to 13C NMR shifts of chalcones and their thiophene and furan analogues: A useful tool for the shift assignment and for the study of substituent effects

Abstract

Abstract13C NMR shifts of 54 chalcones and their thiophene and furan analogues are analyzed by principal component analysis. Thus, a mathematical model is derived for the variation of the carbon shifts in each of seven classes. Two component models are found to be adequate by cross‐validation. The first component corresponds to ordinary σpara values, while the second one differentiates benzenes, thiophenes and furans. This type of data analysis is a useful tool for checking the consistencies of spectral parameters. The model parameters, which describe systematic variations within each class, are also used for the study of substituent effects and discussed in relation to substituent constants in linear free energy relationships.