A SIMPLIFIED PROCEDURE FOR THE ANALYSIS OF COMPLEX NUCLEAR MAGNETIC RESONANCE SPECTRA: II. THE ANALYSIS OF SYMMETRICAL TRIFLUOROBENZENE, THE AA′A″XX′X″ SYSTEM

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Abstract
The analysis of the six spin AA′A″XX′X″ system consisting of two sets of three chemically equivalent nuclei with spin [Formula: see text] and four coupling constants JAA, JXX, JAX, and JAX′ has been developed with the use of group theory and the appropriate Hamiltonian. It is found that there will be differences in the A and X spectra if JAX ≠ JAX′ and simultaneously JAA ≠ JXX. If JAA = JHH the A and X spectra become identical. If JAX = JAX′ each spectrum of course becomes trivial.The complex n.m.r. spectrum of the AA′A″XX′X″ can be decomposed into subspectra, and the analysis of the nuclear magnetic resonance spectra of symmetrical trifluorobenzene has been carried out in this manner. The experimental proton and fluorine spectra of this molecule exhibit marked differences. Calculated spectra have been fitted to the experimental spectra and the following values of the coupling constants have been found:[Formula: see text]The sign of JHH is the same as the sign of JHF•JHF and JHF′ have opposite signs. It is not possible to relate the signs of JHH and JFF to the signs of JHF and JHF′ in this type of spectrum. However, comparison of the signs of couplings in related molecules suggest that JHF, JHH, and JFF have the same sign.