Optimization of the Cyclic Cross-Hyperconjugation in 1,4-Ditetrelcyclohexa-2,5-dienes
Optimization of the Cyclic Cross-Hyperconjugation in 1,4-Ditetrelcyclohexa-2,5-dienes
复制标题
DOI：
10.1021/om5001875
复制
发表时间：
2014-06-23
期刊：
影响因子：
2.8
通讯作者：
Ottosson, Henrik
中科院分区：
文献类型：
--
作者：
Emanuelsson, Rikard;Denisova, Aleksandra V.;Ottosson, Henrik
环状交叉超共轭可以不同程度地存在于 1,4-二四环己环己-2,5-二烯中，即全碳环己-1,4-二烯和 1,4-disila/digerma/distanna/diplumbacyclohexa-2,5-二烯。在本研究中，我们首先使用密度泛函理论（DFT）计算，通过寻找两个饱和E（E'Me-3）（2）部分（E和E'作为相同或不同的tetrel（第14族）元素）中的最佳原子E和取代基E'Me-3来优化共轭强度。我们发现，在两个饱和碳原子上逐渐变重的 E'Me-3 取代基的全碳环己二烯表现出显着的交叉超共轭。这些化合物具有两个独立的 C=C 键，其首次电子激发经计算可达到长达 400 nm 的波长（激发能量为 3.1 eV）。这些跃迁大多是禁止的，允许的最低跃迁出现在 387 nm (3.2 eV) 处。硅类似物也是交叉超共轭的，而 1,4-digerma/distanna/diplumbacyclohexa-2,5-diene 则观察到下降。对两种取代的 1,4-二硅杂环六-2,5-二烯的实验证实了 E'Me3 取代基对电子激发和几何形状的影响，分别通过紫外吸收光谱和 X 射线晶体学测定。最后，我们通过计算揭示了C=C双键上的给电子和吸电子取代基如何影响全碳环的电子性质。我们发现第一个计算的激发（被禁止）可以移动到 440 nm（2.83 eV）。这表明环状交叉超共轭可以在多大程度上影响具有两个形式上隔离的 C=C 双键的化合物的电子和光学性质。
Cyclic cross-hyperconjugation can exist to variable extents in 1,4-ditetrelcyclohexa-2,5-dienes, i.e., all-carbon cyclohexa-1,4-dienes and 1,4-disila/digerma/distanna/diplumbacyclohexa-2,5-dienes. In this study we first use density functional theory (DFT) computations to optimize the conjugation strength by seeking the optimal atom E and substituent group E'Me-3 in the two saturated E(E'Me-3)(2) moieties (E and E' as the same or different tetrel (group 14) elements). We reveal that the all-carbon cyclohexadienes with gradually heavier E'Me-3 substituents at the two saturated carbon atoms display significant cross-hyperconjugation. The first electronic excitations in these compounds, which formally have two isolated C=C bonds, are calculated to reach wavelengths as long as 400 nm (excitation energies of 3.1 eV). These transitions are mostly forbidden, and the lowest allowed transitions are found at 387 nm (3.2 eV). The silicon analogues are also cross-hyperconjugated, while a decline is observed in the 1,4-digerma/distanna/diplumbacyclohexa-2,5-diene. Experiments on two substituted 1,4-disilacyclohexa-2,5-dienes confirm the effect of the E'Me3 substituents, with regard to both electronic excitations and geometries as determined by UV absorption spectroscopy and X-ray crystallography, respectively. At the end, we reveal through computations how electron-donating and electron-withdrawing substituents at the C=C double bonds influence the electronic properties of the all-carbon ring. We find that the first calculated excitation, which is forbidden, can be shifted to 440 nm (2.83 eV). This shows to what extent cyclic cross-hyperconjugation can affect the electronic and optical properties of a compound with two formally isolated C=C double bonds.