Interaction of acids with halogenated aromatic compounds. I. Infrared spectrum of hydrogen chloride in fluorobenzene and related solvents

Abstract

The complex infrared absorption band of HCl in fluorobenzene at c. 2800 cm^-1 is due to the presence of three solute species; free molecules in cavities, which produce rotational side bands, molecules hydrogen- bonded to fluorine which give a sharp absorption band, and molecules bonded to the aromatic π-electron system which contribute a broader, overlapping band at lower frequency. Similar multiple absorptions are found for solutions of HCl and DCl in other fluorinated aromatics, and the asymmetry of the central absorptions for these solutes in chloro-, bromo-, and iodo-benzenes is attributed to an unresolved overlap of absorption bands due to halogen-bonded and T-bonded solute. The specific solvent-solute interaction theory of Bellamy for the infrared spectra of solutes in mixed solvents is thus extended to single solvents containing structures which give slightly different interaction energies with the solute.