dl－2，3－二氰基－2，3－二（3，4－二甲氧基苯基）丁二酸二乙酯的晶体和分子结构

Crystal and Molecular Structure of Poly-substituted Bibenzil

用Ｘ射线晶体结构测定和分析了ｄｌ－２，３－二氰基－２，３－二（３，４－二甲氧基苯基）丁二酸二乙酯的分子和晶体结构。晶体学数据为Ｃ（２６）Ｈ（２８）Ｎ２Ｏ８，Ｍｒ＝４９６．５２，空间群Ｐｌ，ａ＝１２．０４７（１）Ａ，ｂ＝１３．２７１（１）Ａ，ｃ＝８．７２８（２）Ａ，α＝９０．７１（１）°，β＝１０８．８１（１）°，γ＝８４．８７（１）°，Ｖ＝１ ３１５．４（２）Ａ３，Ｚ＝２，Ｄｃ＝１．２５４ｇ．ｃｍ（－３）．计算表明分子内有许多非键连原子间距小于ｖａｎｄｅｒＷａａｌｓ半径和，基团间的空间排斥作用使两苄碳原子间的σ键键长较正常的碳－碳单键键长明显增长，且分子内苯环上取代基的电子效应对上述σ键的变化亦有较大影响．

The crystal and molecular structure of dl-diethyl-2, 3-dicyano-2, 3-di ( 3, 4-dimethoxyphenyl) succinate 1 was determined and analyzed. C_26H28N2O8 ,Mr=496. 52, P1a=12. 047 (1) A, b=13. 271 (1) A, c=8. 728 (2) A, a=90. 71 (1)°, β=108. 81(1)° , γ=84. 87 (l)°, V=1315. 4(2)A￣3, Z=2, Dc=1. 254 g/cm￣3, μ(CuKa)=7. 42 cm -1, R=0. 060 (Rw=0. 054) for 3566 observed reflections. In comparison with normal C-C single bond (1. 544A) , the bond length of compound 1 for C(1)-C(14) was remarkably lengthened by 0.037A. The distances between some nonbonding atoms are smaller than the sums of van der Waals radii, indicating the existence of serious steric hindrance in molecule which was mainly responsible for the lengthening effect. The influence of electron effect on C(1)-C(14) bond is discussed.