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首页> 外文期刊>Chemistry: A European journal >Direct Estimate of the Strength of Conjugation and Hyperconjugation by the Energy Decomposition Analysis Method
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Direct Estimate of the Strength of Conjugation and Hyperconjugation by the Energy Decomposition Analysis Method

机译：能量分解分析法直接估算共轭和超共轭强度

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摘要

The intrinsic strength of JT interactions in conjugated and hypercon-jugated molecules has been calculated using density functional theory by energy decomposition analysis(EDA)of the interaction energy between the conjugating fragments.The results of the EDA of the fram--polyenes H_2C= CH-(HC=CH)_n-CH=CH_2(n = l-3)show that the strength of ji conjugation for each C=C moiety is higher than in trans-1,3-butadiene.The absolute values for the conjugation between Si= Si pi bonds are around two-thirds of the conjugation between C=C bonds but the relative contributions of DELTA E_(pi)to DELTA E_(orb)in the all-silicon systems are higher than in the carbon compounds.The IT conjugation between G=C and C=O or C=NH bonds in H_2C=CH-C(H)=O and H_2C=CH-C(H)=NH is comparable to the strength of the conjugation between C=C bonds.The JT conjugation in H_2C=CH-C(R)=O decreases when R = Me,OH,and NH_2 while it increases when R = halogen. The hyperconjugation in ethane is around a quarter as strong as the pi conjugation in ethyne.Very strong hyperconjugation is found in the central C-C bonds in cubylcubane and tetra-hedranyltetrahedrane.The hyperconjugation in substituted ethanes X_3C-CY_3(X,Y = Me,SiH_3,F,Cl)is stronger than in the parent compound particularly when X,Y = SiH_3 and Cl.The hyperconjugation in donor-acceptor-substituted ethanes may be very strong;the largest DELTA E_(pi)value was calculated for(SiH_3)_3C-CCl_3 in which the hyperconjugation is stronger than the conjugation in ethene.The breakdown of the hyperconjugation in X_3C-CY_3 shows that donation of the donor-substituted moiety to the acceptor group is as expected the most important contribution but the reverse interaction is not negligible.The relative strengths of the pi interactions between two C=C double bonds,one C=C double bond and CH_3 or CMe_3 substituents,and between two CH_3 or CMe_3 groups,which are separated by one C-C single bond,are in a ratio of 4:2:1.Very strong hyperconjugation is found in HC ident to C-C(SiH_3)_3 and HC ident to C-CCl_3.The extra stabilization of alkenes and alkynes with central multiple bonds over their terminal isomers coming from hyperconjugation is bigger than the total energy difference between the isomeric species.The hyperconjugation in Me-C(R)=O is half as strong as the conjugation in H_2C= CH-C(R)=O and shows the same trend for different substituents R.Bond energies and lengths should not be used as indicators of the strength of hyperconjugation because the effect of a interactions and electrostatic forces may compensate for the hyperconjuga-tive effect.
机译：通过对结合片段之间的相互作用能进行能量分解分析（EDA），利用密度泛函理论计算了共轭和超共轭分子中JT相互作用的内在强度.fram-多烯H_2C = CH的EDA结果-（HC = CH）_n-CH = CH_2（n = 1-3）表明，每个C = C部分的ji共轭强度均高于反式1,3-丁二烯。 Si = Si pi键大约是C = C键之间共轭的三分之二，但在全硅体系中DELTA E_（pi）对DELTA E_（orb）的相对贡献高于碳化合物。在H_2C = CH-C（H）= O和H_2C = CH-C（H）= NH中，G = C和C = O或C = NH键之间的共轭强度与C = C键之间的共轭强度相当。当R = Me，OH和NH_2时，H_2C = CH-C（R）= O的JT共轭降低，而当R =卤素时，JT共轭升高。乙烷中的高共轭强度比乙炔中的pi共轭强度强四分之一;在立方古巴和四面体四氢呋喃中的中央CC键中发现非常强的超共轭强度;取代的乙烷中的高共轭X_3C-CY_3（X，Y = Me，SiH_3 ，F，Cl）比母体化合物更强，特别是当X，Y = SiH_3和Cl时。供体-受体取代的乙烷的超共轭作用可能非常强;计算出（SiH_3）的最大DELTA E_（pi）值_3C-CCl_3，其中高共轭作用比乙烯中的共轭作用强。X_3C-CY_3中的高共轭作用的分解表明，如预期的那样，将供体取代基团捐赠给受体基团是最重要的贡献，但反向相互作用并非如此两个C = C双键，一个C = C双键和CH_3或CMe_3取代基之间，以及两个CH_3或CMe_3基团之间被一个CC单键隔开的pi相互作用的相对强度在HC ident与CC（SiH_3）_3和HC ident与C-CCl_3的比率为4：2：1。非常强的超共轭作用是由于超共轭作用导致的末端异构体上具有中心多重键的烯烃和炔烃的额外稳定性为Me-C（R）= O的超共轭强度是H_2C = CH-C（R）= O的共轭强度的一半，并且对不同的取代基R表现出相同的趋势。键的能量和长度不应用作超共轭强度的指标，因为相互作用和静电力的作用可能会补偿超共轭作用。

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