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一般情况下双取代乙烯衍生物的反式构象要比顺式构象稳定.但是例外也存在,例如1,2-二氟乙烯和1,2-二氯乙烯.这种双取代乙烯衍生物顺式构象的超常稳定性被称之为顺式效应.该效应的起源和本质目前仍没有定论.本文以12个体系(XHC=CHY(X,Y=F,Cl,Br,CN,CH3,C2H6,OCH3))为例,对顺式效应的有效性、起源和本质进行系统的密度泛函理论研究,其中9个体系存在顺式效应,另外3个为正常体系没有该效应.采用一系列泛函和基组研究其有效性,并运用四种分析手段,如自然键轨道(NBO)、能量分量分析(EDA)、密度泛函活性理论(DFRT)和非共价相互作用(NCI)分析,剖析该效应的起源和本质.发现在顺式构象的两个取代基之间存在一种微弱的非共价相互吸引作用.能量分析表明,静电效应、立体效应等对顺式效应的存在都起着重要作用,但是它们均不能单独用来解释顺式效应的起源.也就是说顺式效应没有一个简单的起源,它是多种作用合力的结果.本文采用双变量解释得到比较合理的相关回归系数R2=0.86-0.87,较好地解释了顺式效应的本质和起源.
In general, the trans conformation of the disubstituted ethylene derivative is more stable than the cis conformation, except for the presence of, for example, 1,2-difluoroethylene and 1,2-dichloroethylene This bis-substituted ethylene derivative, cis The extraordinary stability of the conformation is called the cis-effect. The origin and nature of the effect is still inconclusive. In this paper, 12 systems (XHC = CHY (X, Y = F, Cl, Br, CN, CH3, C2H6, OCH3)) as an example, we systematically studied the validity, origin and essence of cis-effect, including nine cis-acting effects and the other three normal ones without this effect.Using a series of functional And basic sets to study its effectiveness. Four analytical methods, such as NBO, EDA, DFRT and NCI analysis, The origin and nature of the effect shows that there is a weak non-covalent mutual attraction between the two substituents of the cis-conformation. The energy analysis shows that the electrostatic effect, the stereoscopic effect and the like all play a role in the existence of the cis-effect But they can not be used alone to explain the origin of the cis-effect. No effect of a simple origin, it is the result of various forces acting paper bivariate correlation reasonable interpretation is the regression coefficient R2 = 0.86-0.87, can explain the nature and origin of cis effect.