The structures of core-links Al(13) (C-Al(13)) and flat-Al(13) (F-Al(13)) complexes in aqueous solution have been investigated using density functional theory (DFT) at the level of B3LYP/6-31G(d). The present work focuses on the following three aspects: (1) C-Al(13)(9+) was optimized with the consideration of solvent effect and the (27)Al NMR chemical shifts using Hartree Fock GIAO and B3LYP GI...

A current-density functional theory for the calculation of nuclear magnetic resonance chemical shifts is presented. If the Kohn–Sham orbitals are expanded in a finite basis set, one of the main problems is the strong dependency of the results with respect to a shift of the gauge origin of the vector potential which describes the external magnetic field. Two computational schemes implementing bo...

Detailed investigation of the tautomerism of oxazolidines, thiazolidines and selenazolidines substituted at positions 2 and 4 by hydroxy and amino groups was carried out by calculations at HF and MP2 levels of theory and NMR spectroscopy. The relative stabilities of the tautomers of the heterocycles were calculated in gas phase and in solvents CHCl3 and DMSO utilizing the PCM method. The ab ini...

nowadays nmr spectroscopy becomes a powerful tool in chemistry because of the nmr chemical shifts. hartree–fock theory and the gauge-including atomic orbital (giao) methods are used in the calculation of 29si nmr chemical shifts of various silicate species in the silicate solution as initial components for zeolite synthesis both in gas and solution phase. calculations have been performed at geo...

Using the DP4f GIAO-NMR method, the stereochemistry of hemicalide was computationally analysed, resulting in a reassignment at C18 as supported by improved NMR shift correlations with a model C13-C25 fragment 23. An advanced C16-C28 subunit 6 of this potent anticancer agent was then synthesised with the revised 18,19-syn relationship.

The aim of this work is to convince practitioners of (31)P NMR methods to regard simple GIAO quantum chemical calculations as a safe tool in structural analysis of organophosphorus compounds. A comparative analysis of calculated GIAO versus experimental (31)P NMR chemical shifts (CSs) for a wide range of phosphorus containing model compounds was carried out. A variety of combinations (at the HF...

Scoring permutations of experimental chemical shift deviations and DFT/GIAO calculated deviations of isotropic shieldings for sets of four diastereomers can help to assign their relative configurations. This method was exercised on a set of diastereomeric Cinchona alkaloid derivatives, where 13C NMR data always identified the proper configuration. The presented approach is also an attempt to qu...

Accurate (rms error ∼3 ppm) predictions of 13C chemical shifts are achieved for many of the common structural types of organic molecules through empirical scaling of shieldings calculated from gauge including atomic orbitals (GIAO) theory with a small basis set and with geometries obtained from computationally inexpensive molecular mechanics methods. Earlier GIAO calculations are shown to be mu...

Tiếp nối bài 1 và 2 tổng quan các cách tiếp cận khác nhau của học giả nhau, đồng thời, đề xuất thức xem xét chiều qui chiếu ‘Biểu hiện’ (văn hoá) trong tam diện (3-D approach) tác giả, bài viết này tập trung vào ‘Tác động’ (giao tiếp): đưa ra kiểu mô hình giao chính yếu (mô truyền tải, tương tác, xuyên tác), phân loại một số hình/hệ hình/mạng liên văn hoá dân tộc phổ dụng (giả định hệ Chen &amp...