Conformational, Concomitant Polymorphs of 4,4-Diphenyl-2,5-cyclohexadienone: Conformation and Lattice Energy Compensation in the Kinetic and Thermodynamic Forms

4,4‐Diphenyl‐2,5‐cyclohexadienone (1) crystallized as four conformational polymorphs and a record number of 19 crystallographically independent molecules have been characterized by low‐temperature X‐ray diffraction: form A (P21, Z′=1), form B (P$\bar 1$, Z′=4), form C (P$\bar 1$, Z′=12), and form D (Pbca, Z′=2). We have now confirmed by variable‐temperature powder X‐ray diffraction that form A is the thermodynamic polymorph and B is the kinetic form of the enantiotropic system A–D. Differences in the packing of the molecules in these polymorphs result from different acidic CH donors approaching the CO acceptor in CH⋅⋅⋅O chains and in synthons I–III, depending on the molecular conformation. The strength of the CH⋅⋅⋅O interaction in a particular structure correlates with the number of symmetry‐independent conformations (Z′) in that polymorph, that is, a short CH⋅⋅⋅O interaction leads to a high Z′ value. Molecular conformation (Econf) and lattice energy (Ulatt) contributions compensate each other in crystal structures A, B, and D resulting in very similar total energies: Etotal of the stable form A=1.22 kcal mol−1, the metastable form B=1.49 kcal mol−1, and form D=1.98 kcal mol−1. Disappeared polymorph C is postulated as a high‐Z′, high‐energy precursor of kinetic form B. Thermodynamic form A matches with the third lowest energy frame based on the value of Ulatt determined in the crystal structure prediction (Cerius2, COMPASS) by full‐body minimization. Re‐ranking the calculated frames on consideration of both Econf (Spartan 04) and Ulatt energies gives a perfect match of frame #1 with stable structure A. Diphenylquinone 1 is an experimental benchmark used to validate accurate crystal structure energies of the kinetic and thermodynamic polymorphs separated by