COLLISION COMPLEXES .2. H-1 NUCLEAR MAGNETIC-RESONANCE STUDY OF THE COMPLEX CAFFEINE-BENZENE

The collision complexes formed by caffeine and benzene in solutions of carbon tetrachloride were studied by means of NMR spectroscopy over a very wide benzene concentration range (up to a molality of 39.2). The ring current shifts of the resonances can only be interpreted on the basis of a mixture of 1:1 and 1:2 complexes. Both graphical (projection maps) and fairly sophisticated automatic minimization procedures were employed for the first time to extract equilibrium parameters from this type of NMR data. The successful fit of our data suggests that other systems that also show unaccountable differences in formation constants measured from different nuclei of the some acceptor molecule may contain complexes with a molar ratio different from 1:1. © 1979 American Chemical Society.