The adduct 1,4‐benzoquine · TiCl ₄ has been prepared in CH₂Cl₂ solution at about −60°. Its IR. spectrum has been recorded at the same temperature. The experimental study of the vibrational frequencies has been completed by the calculation of the fundamental vibrations in the molecular plane, using Wilson's FG method, with slightly simplified models of 1,4‐benzoquinone · TiCl₄ (13 masses) and 1,4‐benzoquinone · 2TiCl₄ (14 masses); analysis by use of internal and symmetry coordinates. An assignment of most of the observed bands is proposed and the conclusion is reached that the complex, when solid, is (1,4‐benzoquinone · TiCl₄)_n.

The force constants F (C=O) are 9,85 · 10⁵ dyne/cm for the quinone and 8,8 · 10⁵ dyne/cm for the disturbed carbonyl bond of the polymerized complex in the model proposed.

At ordinary temperature in benzene solution of the components the adduct 1,4‐benzoquinone · TiCl₄ · benzene precipitated; with the help of the models, the fundamental vibrations of its IR. spectrum have been assigned.