NMR analyses of cyclodextrin complexes with substituted benzoic acids and benzoate anions

Inclusion modes of alpha-cyclodextrin with para-substituted benzoic acids ( X=H, OH, CH3, CN, NO2) and the corresponding anions are analyzed with NOEs from ROESY experiments and with H-1 NMR shielding variations. The data indi cate a predominant deep inclusion of the carboxy group in the complexes wit h all substituted benzoic acids, irrespective of the nature of the substitu ents. Protons in ortho- and meta-positions to the carboxylic group show com plexation shifts larger than medium-induced shifts observed for any solvent . Complexation-induced C-13 NMR shift (CIS) changes of the phenyl derivativ es are also measured, with partial correction of literature signal assignme nts. Measurements of the same derivatives in several aprotic solvents revea l no correlation with complexation induced shifts, showing that polarity ef fects resulting from the medium cannot be the major source of the observed CIS values.