13304-12-6Relevant articles and documents
Conformational, concomitant polymorphs of 4,4-diphenyl-2,5- cyclohexadienone: Conformation and lattice energy compensation in the kinetic and thermodynamic forms
Roy, Saikat,Banerjee, Rahul,Nangia, Ashwini,Kruger, Gert J.
, p. 3777 - 3788 (2006)
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 (P2 1, Z′=1), form B (P1, Z′ = 4), form C (P1, Z′=12), and form D (Phca, 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 con formation. 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 mol1, the metastable form B = 1.49 kcal mol-3, 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 U latt determined in the crystal structure prediction (Cerius 2, COMPASS) by full-body minimization. Re-ranking the calculated frames on consideration of both Econf (Spartan 04) and U latt 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 -1 (～1.3kJ mol-1).
Reactions of 4,4-Diphenylcarbena-2,5-cyclohexadiene and Related Systems in Dimethyl Sulfoxide
Freeman, Peter K.,Tafesh, Ahmed M.,Clapp, Gary E.
, p. 782 - 789 (2007/10/02)
Thermal decomposition of the lithium salt of the tosylhydrazone of 4,4-diphenyl-2,5-cyclohexadienone (10) in dimethyl sulfoxide produces 4,4-diphenyl-2,5-cyclohexadienone, p-benzylbiphenyl, 3,4-diphenyltoluene, 6,6-diphenyl-1-methylene-2,4-cyclohexadiene, and o-terphenyl, while similar treatment of the lithium salt of the tosylhydrazone of 4,4-diphenylcyclohexenone (26) generates 4,4-diphenylcyclohexenone, 5,5-diphenyl-1,3-cyclohexadiene, 4,4-diphenyl-1-methylene-2-cyclohexene, and 6,6-diphenyl-1-methylene-2-cyclohexene.Thermolysis of the lithium salt of the tosylhydrazone of 4,4-diphenylcyclohexanone (32) in dimethyl sulfoxide yields 4,4-diphenylcyclohexene, 4,4-diphenylcyclohexanone, and 4,4-diphenyl-1-methylcyclohexanol.The kinetics of the thermal decomposition of tosylhydrazone lithium salts 10, 26, and 32 in dimethyl sulfoxide in the temperature range 90-125 deg C were analyzed by evaluating the rate constants for the two consecutive first-order steps.The second step, for parent salts 10, 26, and 32, decomposition of diazo compound to carbene, exhibited values for k2 (110 deg C) of 8.22, 197, and 363 h-1, ΔG(activ)s of 27.2 +/- 3.1, 24.8 +/- 3.1, 24.2 +/- 0.9 kcal mol-1, and Δ(activ)s of -10.7 +/- 5.7, -6.3 +/- 5.8, and -8.1 +/- 1.7 eu.The activation parameters for decomposition of the diazo compounds are interpreted in terms of an increasing dipole moment in the transition state relative to ground state.Product formation from carbene intermediate is viewed in terms of a competition of a singlet oxygen abstraction reaction with intersystem crossing to triplet.
