Additivity of substituent effects upon proton–fluorine coupling constants in polysubstituted fluorobenzenes
Abstract
Substituent effects upon JFH values in polysubstituted fluorobenzenes are demonstrated to be additive for the substituents F, Cl, Br, I, NO2, NMe2, and OMe. An evaluation of the substituent constants by a regression analysis allows the accurate calculation of 230 JFH values in 70 compounds. The consequences of this analysis for the resolution of the ambiguities in the assignment of 3JFH and 4JFH values, and of the sign of 5JFH in many reported JFH values are discussed. The variation of the substituent constants with substituent electronegativity, EX, are considered and an assessment of the literature reports of the correlation of JFH with EX is made.