Shishkina Svetlana V, Shishkin Oleg V, Desenko Sergey M, Leszczynski Jerzy
STC Institute for Single Crystals, National Academy of Sciences of Ukraine, 60 Lenina Avenue, Kharkiv 61001, Ukraine.
J Phys Chem A. 2008 Jul 31;112(30):7080-9. doi: 10.1021/jp802279x. Epub 2008 Jul 10.
The equilibrium geometry, ring-inversion pathway barriers for analogues of cyclohexene with an exocyclic double bond have been studied using the MP2/6-311 G(d,p) level of theory. The equilibrium conformation of the ring depends on conjugation between the endocyclic and exocyclic double bonds. Interactions between conjugated double bonds include the pi-pi conjugation and interactions between the lone pair of the heteroatom of the exocyclic double bond and the sigma-antibonding orbital of the endocyclic single bond. In the case of the tetrahydrocycles with double bonds separated by a methylene group the balance between the pi --> sigma* hyperconjugation interactions between the exocyclic double bond and the neighboring methylene group and the n --> sigma* interaction between the lone pair of the heteroatom and the sigma-antibonding orbitals of the C(sp(2))-C(sp(3)) bond determine the geometrical parameters of the ring. The character of the potential-energy surface around the saddle point depends on the position of the exocyclic double bond and the orientation of the hydrogen atom attached to the heteroatom of the V group of the periodic table in the tetrahydrocycles with double bonds separated by a methylene group.
利用MP2/6 - 311G(d,p)理论水平研究了具有环外双键的环己烯类似物的平衡几何结构、环反转途径势垒。环的平衡构象取决于环内双键和环外双键之间的共轭作用。共轭双键之间的相互作用包括π - π共轭以及环外双键杂原子的孤对电子与环内单键的σ反键轨道之间的相互作用。在双键被亚甲基隔开的四氢环的情况下，环外双键与相邻亚甲基之间的π→σ超共轭相互作用以及杂原子孤对电子与C(sp(2)) - C(sp(3))键的σ反键轨道之间的n→σ相互作用的平衡决定了环的几何参数。在双键被亚甲基隔开的四氢环中，鞍点周围势能面的特征取决于环外双键的位置以及与元素周期表V族杂原子相连的氢原子的取向。
