The discovery of two isomerstrans(m.p. 332°) andsyn(m.p. 255°) of the title compound and the assignment of conformations to them is due to Schönberg, Sodtke&Praefcke [Chem. Ber.(1969), 102, 1453]. X‐ray structure analysis confirms the assignment. Thesynisomer, which is converted quantitatively totranswhen molten, crystallizes inP21/cwithZ= 8 and thus has two asymmetric molecules per general position. Thetransisomer also crystallizes inP21/cbut withZ= 2 so that the molecule is centrosymmetric. Molecules of both isomers are severely overcrowded and their geometry is discussed. Thetransisomer has probably the lower free energy at all temperat