1H- 1H Inter-ring coupling constants in isoquinoline and quinazoline. Their relationship with corresponding 19F- 19F couplings in perfluoro derivatives

Abstract

Complete spectral analysis of 1H NMR spectra of isoquinoline and quinazoline is performed. Signs of inter-ring coupling constants ( J HH ir) are determined by INDOR experiments. The mechanisms of transmission of J HH ir are discussed. A linear correlation exists between the majority of J HH ir of quinoline, isoquinoline, and quinazoline and J HH ir of their perfluoroderivatives; exceptions are rationalized. The linear relationship with the near-zero value of intercept J HH ir = 0.02 4 + 0.04 0 J HH ir strongly suggests that J HH ir originate, almost quantitatively, from the Fermi contact term and are transmitted via the π-electron system, except for the peri J HH ir. A computation of the proportionality between J HH ir and J HH ir in quinoline using the Pople and Santry expression for the contribution of π electrons to interring coupling constants gives results which are in satisfactory agreement with those observed experimentally.