The Ebind values for C6H5X–C6H6 pff dimers (a) can be approximated very well as the Ebind values for HX–C6H6 complexes (b) where the X substituents in C6H5X and HX are the same. This supports the notion that the strength of substituted benzene–benzene interactions are dictated by the interaction between the substituent and the adjacent benzene ring.54