1:1 or 1:2 solid stoichiometric adducts of TiCl4 with anthraquinone‐1,4, anthraquinone‐1,2, naphtacenequinone‐5,12, pentacenequinone‐6,13 have been prepared. The very important lowering Δω(CO) of the respective IR. carbonyl frequencies, ranging from −160 to −100 cm−1, shows that the acceptor is linked by a dative bond to the carbonyl oxygen atom acting as donor. On the basis of calculations and various considerations, the reduction of the CO double bond character is confirmed. Linear relations are found to exist between the oxydo‐reduction or the polarographic reduction potential of the quinones, and their antisymetric ωa(CO) frequencies, the values of Δω, and the O → Ti vibrations, respectively.