The spectra of halogen substituted salicylanilides

The examination of a comprehensive set of halogen substituted salicylanilides by infra-red and ultraviolet spectroscopy shows that the molecules substituted in the 2′ position of the anilide ring form a special sub-group of salicylanilides because of their intramolecular NH—Halogen bonding. Even so, G eiger 's suggested structures for the α and β forms are probably correct. The primary reason for the excessive steric hindrance which causes the breakage of the chelate ring is the bonding of the proton accepting solvent to the NH group. The probability factor for the breakage of the chelate ring depends on the acidity of the OH group and the bridge strengthening properties of the substituents on the anilide ring. A possible structure for the salicylanilide ion is suggested.