Rastrelli Federico, Bagno Alessandro
Dipartimento di Scienze Chimiche, Università di Padova via Marzolo, 1, 35131 Padova (Italy), Fax: (+39) 049-827-5239.
Chemistry. 2009 Aug 10;15(32):7990-8004. doi: 10.1002/chem.200802443.
Nuclear shieldings, including the Fermi contact and pseudocontact terms, have been calculated with DFT methods in a variety of open-shell molecules (nitroxides, aryloxyl and various transition-metal complexes), thereby predicting (1)H and (13)C chemical shifts. In general, when experimental data are reliable a good agreement with experimental values is observed, thus demonstrating the predictive power of DFT also in this context. However, the general accuracy is lower than that for closed-shell species. A few inconsistencies in literature values are reconciled by reassigning some shifts. Structural, magnetic, and dynamic parameters have also been put into the Solomon-Bloembergen equations to predict signal line shapes, in particular those of signals that are difficult to locate or are undetectable. Guidelines are provided to predict the order of magnitude of relaxation rates. It is shown that DFT-predicted paramagnetic shifts can greatly assist in obtaining and understanding the NMR spectra of paramagnetic molecules, which generally require different experimental strategies and exhibit problems in detection and assignment.
已使用密度泛函理论（DFT）方法计算了包括费米接触项和赝接触项在内的核屏蔽，涉及多种开壳层分子（氮氧化物、芳氧基和各种过渡金属配合物），从而预测了氢-1（¹H）和碳-13（¹³C）的化学位移。一般来说，当实验数据可靠时，会观察到与实验值的良好一致性，这也证明了DFT在这种情况下的预测能力。然而，总体精度低于闭壳层物种。通过重新指定一些化学位移，调和了文献值中的一些不一致之处。还将结构、磁性和动力学参数代入所罗门-布洛姆伯根方程以预测信号线形状，特别是那些难以定位或无法检测到的信号的形状。文中提供了预测弛豫速率量级的指导原则。结果表明，DFT预测的顺磁位移可极大地有助于获取和理解顺磁分子的核磁共振谱，这类谱通常需要不同的实验策略，并且在检测和归属方面存在问题。
