Nikolova Valia, Ilieva Sonia, Galabov Boris, Schaefer Henry F
Department of Chemistry, University of Sofia , 1 James Bourchier Avenue, Sofia 1164, Bulgaria.
J Org Chem. 2014 Aug 1;79(15):6823-31. doi: 10.1021/jo500732m. Epub 2014 Jul 16.
IR spectroscopic experiments and theoretical DFT computations reveal the effects of aromatic substituents on π-hydrogen bonding between monosubstituted phenol derivatives and benzene. Simultaneous formation of two π-hydrogen bonds (red-shifting O-H···π and blue-shifting ortho-C-H···π) contribute to the stability of these complexes. The interaction of the acidic phenol O-H proton-donating group with the benzene π-system dominates the complex formation. The experimental shifts of O-H stretching frequencies for the different phenol complexes vary in the range 45-74 cm(-1). Strong effects on hydrogen-bonding energies and frequency shifts of electron-withdrawing aromatic substituents and very weak influence of electron-donating groups have been established. Experimental quantities and theoretical parameters are employed in rationalizing the properties of these complexes. The acidities of the proton-donating phenols describe quantitatively the hydrogen-bonding process. The results obtained provide clear evidence that, when the structural variations are in the proton-donating species, the substituent effects on π-hydrogen bonding follow classic mechanisms, comprising both resonance and direct through-space influences. The performance of three alternative DFT functionals (B3LYP, B97-D, and PBE0 combined with the 6-311++G(2df,2p) basis set) in predicting the O-H frequency shifts upon complexation is examined. For comparison, O-H frequency shifts for several complexes were also determined at MP2/6-31++G(d,p).
红外光谱实验和理论密度泛函理论（DFT）计算揭示了芳香取代基对单取代酚衍生物与苯之间π-氢键的影响。两个π-氢键（O-H···π红移和邻位C-H···π蓝移）的同时形成有助于这些配合物的稳定性。酸性酚O-H质子供体基团与苯π-体系的相互作用主导了配合物的形成。不同酚配合物的O-H伸缩频率的实验位移在45 - 74 cm⁻¹范围内变化。已确定吸电子芳香取代基对氢键能和频率位移有强烈影响，而供电子基团的影响非常微弱。实验量和理论参数用于合理化这些配合物的性质。质子供体酚的酸度定量描述了氢键过程。所得结果提供了明确的证据，即当质子供体物种存在结构变化时，取代基对π-氢键的影响遵循经典机制，包括共振和直接的空间影响。研究了三种替代DFT泛函（B3LYP、B97-D和PBE0与6-311++G(2df,2p)基组结合）在预测配合时O-H频率位移方面的性能。为了进行比较，还在MP2/6-31++G(d,p)水平上确定了几种配合物的O-H频率位移。
