Department of Chemistry, University of Helsinki , P.O. Box 55, A.I. Virtanens plats 1, FIN-00014 Helsinki, Finland.
Departamento de Ciencias del Ambiente, Universidad de Santiago de Chile (USACH) , Av. Libertador Bernardo O'Higgins 3363, 9170022 Estación Central, Chile.
J Chem Theory Comput. 2017 May 9;13(5):1952-1962. doi: 10.1021/acs.jctc.6b01250. Epub 2017 Apr 4.
Nuclear magnetic shieldings have been calculated at the density functional theory (DFT) level for stacks of benzene, hexadehydro[12]annulene, dodecadehydro[18]annulene, and hexabenzocoronene. The magnetic shieldings due to the ring currents in the adjacent molecules have been estimated by calculating nucleus independent molecular shieldings for the monomer in the atomic positions of neighbor molecules. The calculations show that the independent shielding model works reasonably well for the H NMR shieldings of benzene and hexadehydro[12]annulene, whereas for the larger molecules and for the C NMR shieldings the interaction between the molecules leads to shielding effects that are at least of the same size as the ring current contributions from the adjacent molecules. A better agreement is obtained when the nearest neighbors are also considered at full quantum mechanical (QM) level. The calculations suggest that the nearest solvent molecules must be included in the quantum mechanical system, at least when estimating solvent shifts at the molecular mechanics (MM) level. Current density calculations show that the stacking does not significantly affect the ring current strengths of the individual molecules, whereas the shape of the ring current for a single molecule differs from that of the stacked molecules.
已在密度泛函理论（DFT）水平上计算了苯、十六氢[12]轮烯、十二氢[18]轮烯和六苯并蔻的堆叠的核磁共振屏蔽。通过计算单体在相邻分子的原子位置处的核独立分子屏蔽，估算了相邻分子中环电流引起的磁屏蔽。计算表明，独立屏蔽模型对于苯和十六氢[12]轮烯的 H NMR 屏蔽效果相当有效，而对于较大的分子和 C NMR 屏蔽效果，分子之间的相互作用导致屏蔽效应至少与相邻分子的环电流贡献一样大。当考虑最近邻分子也处于全量子力学（QM）水平时，可获得更好的一致性。计算表明，当在分子力学（MM）水平估计溶剂位移时，必须将最近的溶剂分子包含在量子力学体系中。电流密度计算表明，堆叠不会显著影响单个分子的环电流强度，而单个分子的环电流形状与堆叠分子的环电流形状不同。
