Department of Chemistry, Amherst College, P.O. Box 5000, Amherst, Massachusetts 01002-5000, USA.
J Chem Phys. 2009 Nov 28;131(20):204302. doi: 10.1063/1.3246841.
Guided by ab initio calculations, Fourier transform microwave rotation spectra in the 6.5-22 GHz region are obtained for the complex formed between trans-1,2-difluoroethylene and hydrogen fluoride, including the normal isotopomer and two singly substituted (13)C species in natural abundance. Spectra are also obtained for the analogous three species formed using deuterium fluoride. Analysis of the spectra provides rotational and hyperfine constants that are used to determine a structure for trans-CHFCHF-HF. This structure is similar to that obtained for 1,1-difluoroethylene-HF [H. O. Leung et al., J. Chem. Phys. 131, 204301 (2009)] in that a primary, hydrogen bonding interaction exists between the HF donor and a F atom acceptor on the 1,2-difluoroethylene moiety, while a secondary interaction occurs between the F atom on the HF molecule and the H atom cis to the hydrogen-bonded F atom on the substituted ethylene and causes the hydrogen bond to deviate from linearity. Because the two F atoms and the two H atoms in trans-1,2-difluoroethylene form electrostatically equivalent pairs, the structure of the complex with HF provides insight into the contribution of steric effects to the observed geometries of fluoroethylene-protic acid complexes. A comparison of the observed hydrogen bond lengths and deviations from linearity in 1,1-difluoroethylene-HF and trans-1,2-difluoroethylene-HF suggests that the F atoms in trans-1,2-difluoroethylene are more nucleophilic than those in 1,1-difluoroethylene and that the H atoms are similarly more acidic. Ab initio calculations of electrostatic potentials mapped onto total electron density surfaces for these two molecules support these conclusions.
在从头算的指导下，得到了反式-1,2-二氟乙烯与氟化氢形成的复合物的傅里叶变换微波旋转光谱，包括在天然丰度下的正常同位素体和两种单取代的（13）C 物种，频率范围为 6.5-22GHz。还获得了使用氟化氘形成的类似的三种物种的光谱。对光谱的分析提供了旋转和超精细常数，用于确定反式-CHFCHF-HF 的结构。该结构与 1,1-二氟乙烯-HF [H. O. Leung 等人，J. Chem. Phys. 131, 204301（2009）]获得的结构相似，因为 HF 供体与 1,2-二氟乙烯部分上的 F 原子受体之间存在主要的氢键相互作用，而 HF 分子上的 F 原子与与氢键合的 F 原子处于顺式的 H 原子之间发生次要相互作用，并导致氢键偏离线性。由于反式-1,2-二氟乙烯中的两个 F 原子和两个 H 原子形成静电等效对，因此与 HF 形成的复合物的结构提供了对观察到的氟乙烯-质子酸络合物几何形状的立体效应贡献的深入了解。对 1,1-二氟乙烯-HF 和反式-1,2-二氟乙烯-HF 中观察到的氢键长度和偏离线性的比较表明，反式-1,2-二氟乙烯中的 F 原子比 1,1-二氟乙烯中的 F 原子更具亲核性，而 H 原子也同样更具酸性。这些分子的静电势对总电子密度表面的从头算计算支持了这些结论。
