A proton magnetic resonance study of the systems resorcinol–water and resorcinol–dioxan–water

Abstract

The care necessary in using internal reference compounds in the n.m.r. study of aqueous solutions of aromatic compounds is re-emphasised and a convenient external reference system is recommended. Proton chemical shift data for solutions of resorcinol in water, resorcinol in dioxan, and resorcinol in a number of dioxan–water mixtures are reported. They include the shifts for the water protons, the dioxan protons, and the resorcinol aromatic protons. In general the exchangeable protons (those of the water and the resorcinol hydroxyls) give a single resonance line. Although the observed position of this line moves downfield with increasing resorcinol concentration in aqueous solution, it is concluded that the shift of the water protons is upfield. An upfield movement is also shown by the resorcinol aromatic protons and by dioxan protons in the presence of resorcinol, and is presumably caused by the magnetic anisotropy of the aromatic ring. The present data give no conclusive evidence for hydrophobic bonding in these systems. The dangers in interpreting chemical shift data are discussed, and it is concluded that they provide at best uncertain evidence regarding hydrophobic bonding and the structure of water.