Department of Chemistry, Karadeniz Technical University, 61080, Trabzon, Turkey.
J Mol Model. 2010 Apr;16(4):781-8. doi: 10.1007/s00894-009-0608-9. Epub 2009 Nov 11.
The geometry and electronic structure of exo-tricyclo[3.2.1.0(2,4)]oct-6-ene (exo-TCO) was investigated using DFT methods. The two faces of the endo-pyramidalised double bond of the molecule are not equivalent. The exo face of the double bond has regions with high electron density (q (i,HOMO)) and greater negative potential. Molecular complexes of exo-TCO with bromine were investigated using the B3LYP/6-311++G(d,p) method; the exo-TCO . . . Br(2)(exo) molecular complex was found to be relatively more stable than the exo-TCO . . . Br(2)(endo) complex. The cationic intermediates of the reaction were studied by DFT and MP2 methods. The solvent effect was evaluated using the self-consistent isodensity polarised continuum model (SCI-PCM). The exo-bromonium cation was found to be more stable than the endo-bromonium cation. Exo-facial selectivity due to electronic and steric factors was observed upon addition of bromine to exo-TCO. The multicentre nonclassical delocalised bromocarbonium cation IV and the exo-bridged-bromonium cation I are more stable than the rearrangement cation V. The reaction products are formed via exo-bridged-bromonium I and nonclassical IV cations, which are the most stable intermediates and whose stabilities barely differ. The mechanism of the addition reaction is also discussed.
用 DFT 方法研究了外-tricyclo[3.2.1.0(2,4)]辛-6-烯（外-TCO）的几何形状和电子结构。分子中内-三角锥形双键的两个面不等效。双键的外表面具有高电子密度（q(i,HOMO)）和更大的负电势区域。使用 B3LYP/6-311++G(d,p)方法研究了外-TCO 与溴的分子复合物；发现外-TCO... Br(2)(外)分子复合物比外-TCO... Br(2)(内)复合物更稳定。通过 DFT 和 MP2 方法研究了反应的阳离子中间体。使用自洽等密度极化连续体模型（SCI-PCM）评估了溶剂效应。发现外-溴翁阳离子比内-溴翁阳离子更稳定。由于电子和空间位阻因素，在外-TCO 中加入溴时观察到了外向选择性。多中心非经典离域溴碳阳离子 IV 和外桥接-溴翁阳离子 I 比重排阳离子 V 更稳定。反应产物通过外桥接-溴翁 I 和非经典 IV 阳离子形成，它们是最稳定的中间体，稳定性几乎没有差异。还讨论了加成反应的机理。
