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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Theoretical Study on the Low-Energy and High-Energy Conformers of the Three Isomers of 1,4-Difluorobutadiene
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Theoretical Study on the Low-Energy and High-Energy Conformers of the Three Isomers of 1,4-Difluorobutadiene

机译：1,4-二氟丁二烯的三种异构体的低能和高能构象的理论研究

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摘要

The low-energy and high-energy conformers of the three isomers of 1,4-difluorobutadiene (DFBD) have been investigated with the Gaussian-3 (G3) and G3//B3LYP (G3B3) methods. the geometrical structures of the conformers have been gradient optimized by the HF and B3LYP methods with the 6-31G(d,p) basis set. Natural bond orbital (NBO) analysis has also been performed at the same levels of theory. The computational results show that the high-energy and low-energy conformers of a given isomer is essentially the same in geometry, except that their torsional angles about the C-C bonds are different, and among them only the high-energy conformer of the cis-trans isomer is coplanar. Harmonic vibrational frequency analysis indicates that the high-energy conformers are characterized by their smaller separations of the two C=C stretching modes and the reversed order of the v(C=C)_(sym) and v(C=C)_(asym) peaks compared to that of their low-energy conformer partners. NBO analysis indicates that the #pi#-#pi# conjugative interaction in a high-energy conformer is smaller than that in its low-energy conformer partner and that the significant n-#pi# interactions in the high0-energy conformers contribute to their extra stabilities. Through the G3B3 calculations, the conformational energies of the cis-cis, cis-trans, and trans-trans isomers are estimated to be 17.1, 7.9, and 9.8 kJ mol~(-1), respectively. The stability sequence of the high-energy conformers in different isomers is (cis-trans) > (trans-trans) > (cis-cis), while that of the low-energy conformers is (cis-cis) > (cis-trans)> (trans-trans). The distinctive energy relationships between the conformers of different energy groups are attributed to the intramolecular hydrogen bonds in the high-energy conformers.
机译：1，Gassian-3（G3）和G3 // B3LYP（G3B3）方法研究了1,4-二氟丁二烯（DFBD）三种异构体的低能和高能构象。构象异构体的几何结构已通过HF和B3LYP方法在6-31G（d，p）基础集上进行了梯度优化。自然键轨道（NBO）分析也已在相同的理论水平上进行。计算结果表明，给定异构体的高能和低能构象异构体在几何形状上基本相同，不同之处在于它们围绕CC键的扭转角不同，并且其中只有顺式的高能构象异构体。反式异构体是共面的。谐波振动频率分析表明，高能构象异构体的特征是两个C = C拉伸模式的间距较小，并且v（C = C）_（sym）和v（C = C）_（相较于其低能量符合者的峰值。 NBO分析表明，高能构象体中的#pi＃-＃pi＃共轭相互作用小于其低能构象体伴侣中的相互作用，并且高能构象体中显着的n-＃pi＃相互作用有助于它们的形成。额外的稳定性。通过G3B3计算，顺式-顺式，顺式-反式和反式-反式异构体的构象能量分别估计为17.1、7.9和9.8 kJ mol〜（-1）。高能构象异构体在不同异构体中的稳定顺序为（顺-反）>（反-反）>（顺-顺），而低能构象体的稳定顺序为（顺-顺）>（顺-反） ）>（trans-trans）。不同能量组的构象异构体之间独特的能量关系归因于高能构象异构体中的分子内氢键。

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