ISSN 1017-2548(Print)
ISSN 2234-8530(Online)
Volume 9, Number 4
JKCSEZ 9(4)
August 20, 1965 

Ultraviolet spectrophotometric investigations have been carried out on the systems of benzene with iodine, bromine, chlorine and iodine monobromide in carbon tetrachloride. The results reveal the formation of one to one molecular complexes of the type, C6H6·X2 or C6H6·IX (X denotes halogen atoms). The equilibrium constants obtained at 25°for the complex formation are 0.173, 0.137, 0.0643 and 0.341 lmole-1 for C6H6·I2, C6H6·Br2, C6H6·Cl2 and C6H6·IBr, respectively. These results combined with those obtained by other workers indicate that the relative stabilities of the benzene complexes decrease in the order, ICl > IBr > I2 > Br2 > Cl2. This order may be measure of their relative acidities toward benzene, which is explained in terms of the relative polarizabilities of halogen molecules and the relative electronegativities of halogen atoms.