DIPOLE MOMENT AND STRUCTURE OF HEXACHLORO CYCLOHEXANES

Commercial hexachlorocyclohexane was separated into four isomers : α, β,_. \(\gamma\) and \(\delta\) melting at 158°, 309°, 112.5° and 138⁰ respectively, by fractional crystallisation from methyl alcohol. The aielectric constants and densities of the isomers were measured in different solvents and the dipole moments of the isomrs were calculated by applying the new equation. The results are used to ascribe the structures to the isomers. β and δ isomers have symmetrical structures. The moment 2.55 D of 7-isomer, which has five equatorial and one polar chlorine atoms, is explained as the vector of two C—Cl bonds at tetrahedral angle, the remaining bonds cancelling out. The moment 1.7 D for the α-isomer is explained on the basis of the flexible boat form which has the highest energy content and which forms 70% of the product. The heat of vaporisation of the β-isomer is lowest (11.87 K cal. ) and of others, about 13.6 K cal. The infa-red spectra support the structures assigned to the various isomers. The study of alkaline dehydrochlorination of the isomers indicate the order of hydrolysis as α > δ > \(\gamma\)> ϵ, the β- isomer being inert. The correlation between the insecticidal property and the dipole moment of the isomers reveals the fact that in this series the dipole moment varies linearly with the logarithm of the mortality coefficient K and that the \(\gamma\)-isomer, which possesses outstanding insecticidal properties, has high dipole moment.