19F nuclear magnetic resonance studies of aromatic compounds. Part IV. Transmission of substituent effects across two aromatic rings connected by an N–N linkage

Abstract

The synthesis of several series of dinuclear aromatic compounds of the type p-FC₆H₄·Z·C₆H₄X [graphic omitted] is described. The ¹⁹F n.m.r.spectra are used to examine the transmission of substituent effects, due to the group X, across the bridge Z. It is necessary to distinguish between ‘transmission’(the trans-azo-and-azoxy-series) in which electron density is probably transferred from one ring to the other and ‘relay’(in the cis-azo- and -azoxy-series, and the hydrazo-series) in which the substituent effects most probably occur by modification of the repulsive interaction between the non-bonding lonepairs on the interconnecting nitrogen atoms. Support for this suggestion is given by observation of long range (11 bond) coupling between fluorine nuclei in n.m.r. spectra of the 4,4′-difluoro-members of the ‘transmission’ series and its absence in the spectra of the corresponding members of the ‘relay’ series. A recent examination of long range substituent effects in some analogous series is discussed and the results re-assessed. Some consideration is given to an analogous treatment of ¹³C and ¹H n.m.r. shielding data in some 4-substituted styrene derivatives