Conformational analysis of meso- and (±)-2,3-dicyano-2,3- dicyclopropylbutane and 1,2-dicyanotetracyclopropylethane
作者:Yu-Lin Lam、Ming Wah Wong、Hsing-Hua Huang、Eping Liang
DOI:10.1039/b103740b
日期:——
The dipole moments of meso-2,3-dicyano-2,3-dicyclopropylbutane meso-1, (±)-2,3-dicyano-2,3-dicyclopropylbutane (±)-1 and 1,2-dicyanotetracyclopropylethane 2 in carbon tetrachloride and benzene have been measured over a range of temperatures. Analyses of the relative permittivity data show that at 25 °C, meso-1 and (±)-1 favour the trans form. However, replacement of the methyl groups in 1 with cyclopropyl moieties completely reverses the trans ⇌ gauche equilibrium, such that 2 exists in 74%
gauche conformation. The experimentally derived values of the energy difference between the gauche and trans conformers and the gauche/trans population quotients were compared with values predicted
by molecular orbital calculations. Theory predicts that the conformational preference of the substituted dicyanoethanes is strongly influenced by solvent polarity. The crystal and molecular structures of meso-1 and 2 were determined by single-crystal X-ray diffraction methods. Both compounds exist in the trans conformation in the solid state.
在一定温度范围内测量了介-2,3-二氰基-2,3-二环丙基丁烷介-1、(±)-2,3-二氰基-2,3-二环丙基丁烷(±)-1 和 1,2-二氰基四环丙基乙烷 2 在四氯化碳和苯中的偶极矩。对相对介电常数数据的分析表明,在 25 °C 时,介-1 和(±)-1 更倾向于反式形式。然而,用环丙基取代 1 中的甲基会完全逆转反式 ⇌ 高奇平衡,从而使 2 以 74% 的高奇构象存在。实验得出的高切构象和反式构象之间的能量差值以及高切/反式种群商数与分子轨道计算得出的预测值进行了比较。理论预测,取代的二氰基乙烷的构象偏好受溶剂极性的影响很大。通过单晶 X 射线衍射方法确定了介-1 和介-2 的晶体和分子结构。这两种化合物在固态下均以反式构象存在。