摘要
本人测定了双苯并18冠6(DB18C6),苯并15冠5(B15C5),及其配合物B15C5·Mg(ClO_4)_2的~1H谱,对谱图进行了模拟,求得化学位移和偶合常数,由Karplus公式导出了冠醚中—O—CH_2—CH_7—O—单元中氧原子之间的二面角。应用分子力学对DB18C6,B15C5,B15C5·Mg(ClO_4)_2的溶液构象进行了计算,得到—O—CH_2—CH_2—O—单元的二面角,数值与NMR法相近,两种方法相互验证,为冠醚的溶液构象提供了定量的信息。分子力学计算得到了各自最稳定的构象。结果表明,DB18C6具有近似C_2对称性,B15C5和B15C5·Mg(ClO_4)_2具有近似C_(?)对称性。冠醚中的多个氧原子近似在一个平面上,并形成一个正多边形,络合物B15C5·Mg(ClO_4)_2中Mg^(2+)位于B15C5的正多边形的中央。结果显示溶液中冠醚—O—CH_2—CH_2—O——单元的二面角与晶体中不同,这表明冠醚的溶液构象与晶体结构有些变化,其中,DB18C6的结构变化较为特殊,DB18C6晶体中—O—CH_2—CH_2—0—单元有旁式结构,也有反式结构,而DB18C6的溶液构象中旁式结构占主导优势。
The ~1H NMR spectra of DB18C6, B15C5 and B15C5·Mg(ClO_4)_2 were obtained and the torsional angles of the—O—CH_2—CH_2—O—fragment of the crown ethers were calculated by using the Karplus formula. The Molecular Mechanics was used to calculate the conformations of the crown ethers The most stable conformations were given. Results show that the oxygen atoms of the crown ethers are located on a mean plane and form an approximate regular polygon. In the complex B15C5·Mg(ClO_4)_2, Mg^(++) is located on the mean plane of the five oxygen atoms and at the center of the regular polygon. The structures of the crown ethers in solution are different from those in crystal and the changes of the torsional angels of the—O—CH_2—CH_2—O—fragment were given. There are gauche—and anticonformations of the—O—CH_2—CH_2—O—fragment in crystal of DB18C6, but only gauche—conformation is found in the solution.
基金
国家自然科学基金
