对位取代苯甲酸酯晶体结构研究——Ⅰ.对羟基苯甲酸甲酯p-(OH)C_6H_4CO_2CH_3的晶体结构

对羟基苯甲酸甲酯(p—MHB)晶体结构已用X射线衍射法测定。晶体属单斜晶系,空间群为Cc,晶胞参数:a=13.568(5),b=16.959(7),c=12.458(6),β=130.10(3)°。ρobs=1.361gcm~(-3),Z=12,ρ=1.382 gcm~(-3)。使用CAD4四圆衍射仪和MoKα射线收集强度数据,晶体结构用直接法解出,经全矩阵最小二乘修正,对于1098个I>3σ(I)的衍射点的最后偏离因子R=0.054。晶胞中12个分子分成各自独立的三套坐标排布,且三套p—MHB分子构型基本相同。对位取代的OH和CO_2CH_3基团与苯环共平面,苯环上的碳-碳键长呈现“醌型”缩短。

Studies on the Crystal Structure of P-Substituted BenzoatesⅠ. The Crystal Structure of Methylp-Hydroxybenzoate p-(HO)C_6 H_4 CO_2 CH_3 (p-MHB)

The crystal structure of p -MHB has been determined from three dimensional X-ray data. The crystal belongs to monoclinic system with the space group Cc. The cell dimensions are a = 13.568(5),b = 16.959(7), c = 12.458(6)A , β= 130.10(3)°, V = 2192.9A3, d =1.361g/cm3 (d = 1.382g/cm3 ), and Z = 12. The structure has beensolved by direct method and difference Fourier synthesis from 1098 independent reflections collected on a CAD4 four-circle diffracto-meter with MoKα radiation, and refined by a full matrix least-squares procedure by using the isotropic thermal parameters for the hydrogen atoms and the anisotropic thermal parameters for the non-hydrogen atoms. The final R factor is 0.054 for 1098 observed reflections of I >3 σ(I). The 12 molecules in the cell are arranged in three independent sets with basically the same molecular configurations of p-MHB. The p-substituted OH and CO2CH3 groups are in coplane with the benzene ring. The C - C bond in the p-MHB exhibits a kind of "quinonoid" shortness.