Fiorin Barbara C, Basso Ernani A, Tormena Cláudio F, Rittner Roberto, Abraham Raymond J
Departamento de Quimica, Universidade Estadual de Ponta Grossa, Av. General Carlos Cavalcanti 4748, 84030-900 Ponta Grossa, PR, Brazil.
J Phys Chem A. 2009 Mar 26;113(12):2906-13. doi: 10.1021/jp808048s.
The geometries involved in the conformational equilibria of alpha-fluoroacetophenone, p-nitro-alpha-fluoroacetophenone, and p-methoxy-alpha-fluoroacetophenone were investigated. Theoretical calculations showed that cis and gauche forms (F-C-C=O) are their most stable conformers and that in the vapor phase the gauche conformer is predominant. The three compounds were synthesized, and the conformational behavior in solution was estimated from infrared (IR) and nuclear magnetic resonance (NMR) spectra obtained in solvents of different polarity. Their IR spectra showed one carbonyl absorption for the cis and one for the gauche conformer, and that the cis conformer was preferred in the more polar solvents. (1)J(CF), (2)J(C(O)F), and (2)J(HF) coupling constants were obtained from their NMR spectra, and they also showed a preference for the cis conformer when more polar solvents were used. The vapor phase calculations showed a conformational preference for the gauche form. However, when the solvent effects were included in the calculations, the results were in complete agreement with the experimental data (NMR and IR), the cis conformer being the most stable one.
研究了α-氟苯乙酮、对硝基-α-氟苯乙酮和对甲氧基-α-氟苯乙酮构象平衡中涉及的几何结构。理论计算表明，顺式和gauche式（F-C-C=O）是它们最稳定的构象异构体，且在气相中gauche构象异构体占主导。合成了这三种化合物，并根据在不同极性溶剂中获得的红外（IR）和核磁共振（NMR）光谱估算了溶液中的构象行为。它们的红外光谱显示顺式构象异构体有一个羰基吸收峰，gauche构象异构体有一个羰基吸收峰，且在极性更强的溶剂中顺式构象异构体更受青睐。从它们的核磁共振光谱中获得了(1)J(CF)、(2)J(C(O)F)和(2)J(HF)耦合常数，当使用极性更强的溶剂时，这些耦合常数也显示出对顺式构象异构体的偏好。气相计算表明对gauche式构象有偏好。然而，当计算中包含溶剂效应时，结果与实验数据（核磁共振和红外）完全一致，顺式构象异构体是最稳定的。
