精甲霜灵的电子结构及圆二色谱性质

Theoretical study of the structure and CD spectra of metalaxyl-M

采用量子化学密度泛函理论在B3LYP/6-311++G**水平上对精甲霜灵分子几何构型进行优化;在优化的基础上进行圆二色谱究。计算结果表明:(1)C(8)=O(9)与N(1)、C(3)=O(4)与O(5)之间均存在p—π共轭,N原子上另外2个取代基分别位于苯环上下方为最稳定构型。(2)VCD谱中,C(10)—H沿C(8)—C(10)—O(11)平面的摇摆振动在1020cm-1处存在正性康登效应;垂直于该平面的摇摆振动在1273cm-1处出现负性康登效应。C(2)原子上的C—H摇摆振动在的1334cm-1处存在强的康登效应。C(3)=O(4)在的1788cm-1处出现较强的吸收峰;C(8)=O(9)由于与手性中心的间隔一个N原子,其在VCD谱中未出现康登效应。(3)甲醇溶液中的理论ECD谱,228nm处存在正性康登效应,与实验值符合较好;同时,理论计算还预测标题化合物在201nm处存在负性康登效应。

In this paper, B3LYP/6-311＋＋G＊＊ method was applied to study the geometry of metalaxyl-M. Based on the optimized geometry, Circular Dichroism （CD） spectra was calculated by density functional theory （DFT） and time-dependent density functional theory （TD-DFT） with the same functional and basis sets. The theoretical study demonstrates three results. （1） There is a p-π conjugate system between C（8）=O（9） and N（1）, the same conjugate system also exsits between C（3）=O（4） and 0（5）. The most stable conformation is obtained when other two substituent groups of N atom anchor each side of the benzene ring. （2） Detailed analyses of vibrational circular dichroism （VCD） spectra reveal that positive Cotton effects could be observed at 1020 cm-1, when the wagging vibrating of C（10）--H in accord with the C（8）--C（10）---O（11） plane; on the contrary, negative Cotton effects could be observed at 1273 cm-1, when in perpendicular direction of the C（8）--C（ 10）--O（11 ） plane. The wagging vibrating of C（2）--H could produce a srtong Cotton effects at 1334 cm＂1. The Cotton effect caused by the stretching vibration of C（3）=O（4） could be observed at 1788 cmt; and no Cotton effects cuased by the stretching vibration of C（8）=O（9） in VCD, because there is a barrier between C（8）=O（9） bond and C（2） atom setting up by N atom. （3） In methanol, Electronic Circular Dichroism （ECD） of metalaxyl-M has positive Cotton effects at 228 nm, which is good agree with experimental data. However, negative Cotton effects could be observed at 201 nm.