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首页> 外文期刊>Chemistry: A European journal >Conformational,Concomitant Polymorphs of 4,4-Diphenyl-2,5-cyclohexadienone:Conformation and Lattice Energy Compensation in the Kinetic and Thermodynamic Forms
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Conformational,Concomitant Polymorphs of 4,4-Diphenyl-2,5-cyclohexadienone:Conformation and Lattice Energy Compensation in the Kinetic and Thermodynamic Forms

机译：4,4-二苯基-2,5-环己二酮的构象，伴随多晶型：动力学和热力学形式的构象和晶格能量补偿

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摘要

4,4-Diphenyl-2,5-cyclohexa-dienone(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'=l),form B(P1,Z=4),form C(P1,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 enantio-tropic 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(E_(conf))and lattice energy(U_(latt))contributions compensate each other in crystal structures A,B,and D resulting in very similar total energies:E_(total)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 U_(latt)determined in the crystal structure prediction(Cerius2,COMPASS)by full-body minimization.Re-ranking the calculated frames on consideration of both E_(conf)(Spartan 04)and C_(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 < 0.3 kcal mol~(-1)(approx1.3 kJ mol~(-1)).
机译：通过低温X射线衍射表征了4,4-二苯基-2,5-环己二酮（1）结晶为四个构象多晶型物，并记录了19个晶体学独立分子的记录数量：形式A（P2_1，Z'= l），形式B（P1，Z = 4），形式C（P1，Z'= 12）和形式D（Pbca，Z'= 2）。我们现在通过变温粉末X射线衍射证实：形式A是热力学多晶型物，形式B是对映体系AD的动力学形式。这些多晶型物的分子堆积差异是由于不同的酸性C-H供体在CHO链和合成子中接近C = O受体引起的I-III，取决于分子构象。特定结构中CHO相互作用的强度与该多晶型物的对称独立构象（Z'）的数量有关，也就是说，短CHO相互作用导致较高的Z'晶体结构A，B中的分子构象（E_（conf））和晶格能（U_（latt））贡献相互补偿，和D产生非常相似的总能量：稳定形式A的E_（total）= 1.22 kcal mol〜（-1），亚稳态形式B = 1.49 kcal mol〜（-1）和形式D = 1.98 kcal mol〜 （-1）。消失的多晶型物C被假定为动力学形式B的高Z'高能前体。热力学形式A根据晶体结构中确定的U_（latt）值与第三最低能级匹配通过全身最小化预测（Cerius2，COMPASS）。在考虑E_（conf）（Spartan 04）和C_（latt）能量的情况下对计算的帧进行重新排序，可以得到结构稳定的A＃1帧的完美匹配。图1是用于验证由<0.3 kcal mol〜（-1）（约1.3 kJ mol〜（-1））隔开的动力学和热力学多晶型的准确晶体结构能量的实验基准。

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