Cycloadditions of 16-electron 1,3-dipoles with ethylene. A density functional and CCSD(T) study
Cycloadditions of 16-electron 1,3-dipoles with ethylene. A density functional and CCSD(T) study
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DOI：
10.1021/jo990504j
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发表时间：
1999-09-03
影响因子：
3.6
通讯作者：
Chu, SY
中科院分区：
文献类型：
--
作者：
Su, MD;Liao, HL;Chu, SY
采用密度泛函理论和CCSD(T)计算方法，研究了乙烯与丙烯腈（CNC）、腈亚胺（CNN）、氧化腈（CNO）、重氮甲烷（NNC）、氮（NNN）和氧化亚氮（NNO）在气相中的1,3-偶极环加成（DC）反应。所有的结构，包括前体配合物；在B3LYP/6-31G*水平上进行了完全优化，单点能量在CCSD(T)/6-311G**评估。理论结果表明，腈型分子（CNC、CNN和CNO）的直流电反应活化能很小（5.1 ~ 11 kcal/mol），并且这些反应是非常放热的（-77 ~ -46 kcal/mol）。相比之下，NNC、NNN和NNO的直流反应放热较小（-39 ~ -6.0 kcal/mol），活化势垒较大（13 ~ 29 kcal/mol）。此外，本文的工作还表明，基于Press和Shaik理论的构型混合（CM）模型可以成功地预测直流反应的活化能和反应焓的相对顺序；结合我们的理论计算和CM模型，得出以下结论：一个16电子的1,3偶极子反应物，在末端位置有更多的电正性取代基，将具有较小的单重态-三重态分裂。这将有利于与亲偶极试剂的环加成，并将导致更大的放热性。
The 1,3-dipolar cycloaddition (DC) reactions of ethylene with nitrile ylide (CNC), nitrile imine (CNN), nitrile oxide (CNO), diazomethane (NNC), azine (NNN), and nitrous oxide (NNO) in the gas phase were examined using the density functional theory and CCSD(T) calculations. All of the structures, including the precursor complexes;and the transition structures, were completely optimized at the B3LYP/6-31G* level with single-point energies evaluated at CCSD(T)/6-311G**. The theoretical results suggest that the activation energies for the DC reactions of nitrile-type molecules (CNC, CNN, and CNO) are small (5.1-11 kcal/mol) and these reactions are very exothermic (-77 to -46 kcal/mol). In contrast, the DC reactions of NNC, NNN, and NNO are less exothermic (-39 to -6.0 kcal/mol) and have larger activation barriers (13-29 kcal/mol). Moreover, this work shows that the configuration mixing (CM) model based on Press and Shaik's theory can successfully predict the relative ordering of the activation energy and reaction enthalpies of DC reactions; Combining our theoretical calculations and the CM model, the following conclusion emerges: a 16-electron 1,3-dipole reactant with more electropositive substituents at the terminal positions will possess a smaller singlet-triplet splitting. This will facilitate cycloaddition with the dipolarophile and will result in a larger exothermicity.