Is 2-cyclopropylpropene really gauche?
Is 2-cyclopropylpropene really gauche?
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2-环丙基丙烯真的很俗吗？
DOI：
10.1016/j.saa.2004.10.004
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发表时间：
2005
期刊：
影响因子：
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通讯作者：
Kilway,KathleenV
中科院分区：
文献类型：
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作者：
Durig,JamesR;Zheng,Chao;Marzluf,KathleenR;Marquez,GerardoB;Guirgis,GamilA;Wurrey,CharlesJ;Kilway,KathleenV
在3500 ~ 40 cm −1范围内记录了2-环丙基丙烯（2-CPP，c-C3 H5 C（CH 3）CH 2）的红外光谱，并获得了2-CPP的拉曼光谱（3200- 150 cm −1）和2-CPP在液态氪溶液（-105 ~-150 °C）中的中红外光谱。采用限制性Hartree-Fock（RHF）方法、全电子相关微扰法（MP2（full））和密度泛函理论（DFT）的B3 LYP方法，在6-311+G（2df，2 pd）基组下对该分子进行了从头算计算.实验和计算结果的结合（特别是在较高的基组下）明确地将2-CPP的更稳定构象确定为反式，其中gauche旋转异构体的能量更高，但也是稳定的。该化合物的顺式结构在实验上没有观察到，并且通过计算方法预测为过渡态。通过研究溶解在液态氪中的2-CPP的两组良好分辨的构象双峰的温度变化，确定了构象之间的平均焓差为182± 18 cm −1（2.18±0.22kJmol−1），其中反式构象在流体状态下能量较低，并且是多晶固相中唯一的构象。该焓差对应于含有约55±2%的更稳定的反式旋转异构体形式的2-环丙基丙烯的流体相中的环境温度构象平衡。一个完整的振动分配的反式构象的2-CPP的，许多带的gauche旋转异构体也已被指定。在MP2（full）/6-311+G（d，p）水平上计算了该分子的结构参数、偶极矩和转动常数，并将这些结果以及实验研究的结果与相关化合物的类似结果进行了比较。
Infrared spectra of gaseous and solid 2-cyclopropylpropene (2-CPP, c-C3H5C(CH3)CH2) have been recorded from 3500 to 40cm−1, and Raman spectra (3200–150cm−1) of the liquid as well as mid-infrared spectra of 2-CPP in liquid krypton solution (from −105 to −150°C) were also obtained. Ab initio calculations, with basis sets up to 6-311+G(2df, 2pd), were carried out for this molecule, using the restricted Hartree–Fock (RHF) approach, with full electron correlation by the perturbation method to second order (MP2(full)) and density functional theory (DFT) by the B3LYP method. The combination of the experimental and computational results (particularly with the higher basis sets) unequivocally identifies the more stable conformer of 2-CPP as the trans form, with the gauche rotamer higher in energy, but also stable. The cis structure of this compound is not observed experimentally, and is predicted by the computational approaches to be a transition state. By studying the temperature variation of two well-resolved sets of conformational doublets of 2-CPP dissolved in liquid krypton, an average enthalpy difference between conformers of 182±18cm−1(2.18±0.22kJmol−1) has been determined, with the trans conformation lower in energy in the fluid states, and the sole conformer present in the polycrystalline solid phase. This enthalpy difference corresponds to an ambient temperature conformational equilibrium in the fluid phases of 2-cyclopropylpropene containing approximately 55±2% of the more stable trans rotameric form. A complete vibrational assignment for the trans conformer of 2-CPP is given, and many of the bands of the gauche rotamer have also been assigned. Structural parameters, dipole moments, and rotational constants for this molecule have been calculated at the MP2(full)/6-311+G(d,p) level, and these results—as well as the results from the experimental studies—are compared to similar quantities in related compounds.