Lehrstuhl für Theoretische Chemie, Wilhelm-Ostwald Institut für Physikalische und Theoretische Chemie, Universität Leipzig, D-04103 Leipzig, Germany.
J Am Chem Soc. 2010 Jan 20;132(2):484-94. doi: 10.1021/ja902628n.
We present a theoretical investigation of amide pseudorotaxane IR spectra in the harmonic approximation. In particular, we focus on the effect of axle substitution on the hydrogen bonds that are formed between axle and wheel. Two types of pseudorotaxanes are studied: one with the substituent affecting mostly the axle's carbonyl group and one with the effect influencing primarily the amide NH group. Sizeable red shifts are predicted for the carbonyl stretching frequencies, and large red shifts for the NH stretching frequencies. For the wheel amide groups involved in hydrogen bonding merely with their NH hydrogens, a small shift is observed for the carbonyl stretch mode. A clear relation is observed between the NH stretch shifts and individual hydrogen bond energies. This is confirmed by correlations of the shared electron number with the NH stretch shift showing that this quantity can be taken as an indicator for individual hydrogen bond energies. Axle substitution influences the strengths of the individual hydrogen bonds which is again reflected in the NH stretch frequency shifts. A linear relationship of Hammett's substituent parameters with the NH frequency shifts can be established.
我们在谐波近似下对酰胺类伪轮烷的红外光谱进行了理论研究。特别是，我们关注了轮烷中轴取代对形成的轴与轮之间氢键的影响。研究了两种类型的伪轮烷：一种是取代基主要影响轴的羰基，另一种是取代基主要影响酰胺 NH 基团。预测羰基伸缩频率会有较大的红移，NH 伸缩频率也会有较大的红移。对于仅与 NH 氢原子形成氢键的轮烷酰胺基团，羰基伸缩模式的位移较小。观察到 NH 伸缩位移与单个氢键能之间存在明显的关系。这通过与 NH 伸缩位移相关的共享电子数的相关性得到证实，表明该数量可以作为单个氢键能的指标。轴取代影响单个氢键的强度，这再次反映在 NH 伸缩频率位移上。可以建立与 NH 频率位移的哈米特取代基参数的线性关系。
