Conformational Analysis and Electronic Interactions Laboratory, Institute of Chemistry, University of São Paulo, CP 26077, 05513-970 São Paulo, SP, Brazil.
Conformational Analysis and Electronic Interactions Laboratory, Institute of Chemistry, University of São Paulo, CP 26077, 05513-970 São Paulo, SP, Brazil.
Spectrochim Acta A Mol Biomol Spectrosc. 2019 Mar 5;210:82-97. doi: 10.1016/j.saa.2018.11.010. Epub 2018 Nov 12.
The conformational analysis of some 2‑(methoxy)‑2‑[(4‑substituted)‑phenylsulfanyl]‑(4'‑substituted) acetophenones was performed through infrared (IR) spectroscopic analysis of the carbonyl stretching band (ν), supported by B3LYP/6-31+G(d,p) calculations and X-ray diffraction. Five (1-5) of the seven studied compounds (1-7) presented Fermi resonance (FR) on the ν fundamental transition band. Deuteration of these compounds (1a-5a) precluded the occurrence of FR, revealing a ν doublet for all compounds in all solvents used. The computational results indicated the existence of three conformers (c, c and c) for the whole series whose relative abundances varied with solvent permittivity. The higher ν frequency c conformer was assigned to the higher frequency component of the carbonyl doublet, while both c and c were assigned to the lower frequency one. Anharmonic vibrational frequencies and Potential Energy Distribution (PED) calculations of compound 3 indicated that the combination band (cb) between the methyne δ and one skeletal mode couples with the ν mode giving rise to the FR on the c conformer in vacuum and on the c one in non-polar solvents. The experimental data indicated a progressive increase in c conformer stability with the increase of the solvent dielectric constant, which is in good agreement with the polarizable continuum model (PCM) calculations. The higher ν frequency and the stronger solvation of the c conformer is a consequence of the repulsive field effect (RFE) originated by the alignment and closeness of the CO and CO dipoles. Finally, the balance between orbital and electrostatic interactions dictates the conformational preferences. X-ray single crystal analysis for compound 6 revealed the c geometry in the solid state and its stabilization by CH…O hydrogen bonds.
通过对羰基伸缩带（ν）的红外（IR）光谱分析，并结合 B3LYP/6-31+G(d,p)计算和 X 射线衍射，对一些 2-（甲氧基）-2-[(4-取代）-苯硫基]-（4'-取代）苯乙酮进行了构象分析。在所研究的七个化合物（1-7）中，有五个（1-5）化合物在ν基频跃迁带出现费米共振（FR）。这些化合物的氘代（1a-5a）排除了 FR 的发生，在所有使用的溶剂中，所有化合物都出现了ν双峰。计算结果表明，整个系列存在三种构象（c、c 和 c），它们的相对丰度随溶剂介电常数的变化而变化。较高ν频率的 c 构象被分配给羰基双峰的较高频率分量，而 c 和 c 构象则被分配给较低频率分量。化合物 3 的非谐振动频率和势能分布（PED）计算表明，亚甲基 δ和一个骨架模式之间的组合带（cb）与 ν模式耦合，导致真空状态下 c 构象和非极性溶剂中 c 构象的 FR。实验数据表明，随着溶剂介电常数的增加，c 构象的稳定性逐渐增加，这与极化连续体模型（PCM）的计算结果一致。c 构象的较高ν频率和较强的溶剂化作用是 CO 和 CO 偶极子的排列和接近产生的排斥场效应（RFE）的结果。最后，轨道和静电相互作用之间的平衡决定了构象的偏好。化合物 6 的 X 射线单晶分析表明，c 几何在固态中稳定，并通过 CH…O 氢键稳定。
