Zimmermann Charlotte, Fischer Taija L, Suhm Martin A
Institut für Physikalische Chemie, Georg-August-Universität Göttingen, Tammannstr. 6, 37077 Göttingen, Germany.
Molecules. 2020 Nov 3;25(21):5095. doi: 10.3390/molecules25215095.
The influence of distant London dispersion forces on the docking preference of alcohols of different size between the two lone electron pairs of the carbonyl group in pinacolone was explored by infrared spectroscopy of the OH stretching fundamental in supersonic jet expansions of 1:1 solvate complexes. Experimentally, no pronounced tendency of the alcohol to switch from the methyl to the bulkier -butyl side with increasing size was found. In all cases, methyl docking dominates by at least a factor of two, whereas DFT-optimized structures suggest a very close balance for the larger alcohols, once corrected by CCSD(T) relative electronic energies. Together with inconsistencies when switching from a C4 to a C5 alcohol, this points at deficiencies of the investigated B3LYP and in particular TPSS functionals even after dispersion correction, which cannot be blamed on zero point energy effects. The search for density functionals which describe the harmonic frequency shift, the structural change and the energy difference between the docking isomers of larger alcohols to unsymmetric ketones in a satisfactory way is open.
通过对1:1溶剂化配合物超声速喷射膨胀中OH伸缩基频的红外光谱研究，探讨了远程伦敦色散力对不同大小醇类在频哪酮羰基的两个孤对电子之间对接偏好的影响。实验发现，随着醇类尺寸的增加，并没有明显的从甲基侧切换到体积更大的叔丁基侧的趋势。在所有情况下，甲基对接至少占主导地位两倍，而密度泛函理论（DFT）优化的结构表明，一旦通过耦合簇单双激发加微扰三重激发（CCSD(T)）相对电子能量进行校正，对于较大的醇类，两种对接方式的能量非常接近平衡。再加上从C4醇切换到C5醇时出现的不一致性，这表明即使经过色散校正，所研究的B3LYP尤其是TPSS泛函仍存在缺陷，这不能归咎于零点能效应。寻找能够以令人满意的方式描述较大醇类与不对称酮对接异构体之间的谐波频率位移、结构变化和能量差的密度泛函的工作仍在进行中。
