Knowledge Bank

The $AB2C2$ proton NMR spectra of several monosubstituted benzenes have been fitted by the method of total spectral reproduction, in order to find the unobservable coupling constants. Values of the relative Chemical shifts were obtained, in some cases from appropriately deuterated species, and the coupling constants were adjusted until a “best fit” was observed with the experimental spectrum. The 60 Mc NMR spectra of the following monosubstituted benzenes were fitted reasonably well, and their chemical shifts and coupling constants are judged to be accurate within $\pm 0.5$ cps: iodobenzene, aniline, dimethyl aniline, the triphenyl monopositive and mononegative ions, and triphenylaluminum. The spectra of bromobenzene and anisole could not be fated unambiguously. The chemical shifts of the trityl ions are discussed in terms of ring currents and the charge density estimates of molecular orbital theory, and the couplings are again found for all species to be dominated by the sigma electrons.