The use of the direct and the moment methods in the analysis of N.M.R. spectra of oriented molecules

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Abstract
The direct method of analysis is applied to the spectra of oriented molecules with two and three spins. It is shown that the oriented system of two spins with chemical shift, indirect and direct couplings has an infinite number of solutions from known line positions only. If the intensity information is included in the analysis in terms of the second moment of the spectrum, two sets of solutions are obtained. Tickling can decide which of the two solutions is correct. Similarly, in the three-spin system with C 2 symmetry, chemical shift, direct and indirect couplings, there are two possible solutions from transition frequencies. Here the second moment of the spectrum allows the determination of the correct solution. If the chemical shift is zero, there are in principle four possible solutions for the observed spectrum from line positions and intensities. Two of these solutions are shown to be imaginary. The three-spin system without symmetry can be discussed analytically if only direct coupling is present. However, the spectrum has an infinite number of solutions. The theoretical part is illustrated with practical examples. The spectra of 2,6-dibromopyridine and 1,2,4-trichlorobenzene are studied.