NMR-STUDY OF AROMATIC-AROMATIC INTERACTIONS FOR BENZENE AND SOME OTHER FUNDAMENTAL AROMATIC SYSTEMS USING ALIGNMENT OF AROMATICS IN STRONG MAGNETIC-FIELD

The solvent dependence of proton-proton dipolar couplings in a strong magnetic field was used to characterize the aromatic-aromatic interact ions of benzene, hexafluorobenzene (HFB), naphthalene, and some monosu bstituted benzenes under various conditions. The very accurate analysi s of the spectral parameters of benzene also allowed observation of is otope effects on coupling constants and solvent effects on the C-13 is otope shifts. The results indicate that benzene, naphthalene, and the monosubstituted benzenes favor structures in which the aromatic ring i s parallel-stacked with HFB. According to the concentration-dependent experiments, the benzene-HFB complex behaves like a dimer. For benzene -dimer, benzene-naphthalene, and some benzene-monosubstituted benzene complexes there is evidence for T-shaped structures; for benzene in wa ter no clear preference is seen. The complexes express only in very hi gh concentrations, which means that the interaction has significance o nly in conditions where the entropy of the complex formation is small or is compensated by some other interactions.