NMR spectroscopy has recently been utilized to determine the absolute amounts of organic molecules with metrological traceability since signal intensity is directly proportional to the number of each nucleus in a molecule. The NMR methodology that uses hydrogen nucleus ( 1 H) to quantify chemicals is called quantitative 1 H-NMR ( 1 H qNMR). The quantitative method using 1 H qNMR for determining the purity or content of chemicals has been adopted into some compendial guidelines and official standards. However, there are still few reports in the literature regarding validation of 1 H qNMR methodology. Here, we coordinated an international collaborative study to validate a 1 H qNMR based on the use of an internal calibration methodology. Thirteen laboratories participated in this study, and the purities of three samples were individually measured using 1 H qNMR method. The three samples were all certified via conventional primary methods of measurement, such as butyl p-hydroxybenzoate Japanese Pharmacopeia (JP) reference standard certified by mass balance; benzoic acid certified reference material (CRM) certified by coulometric titration; fludioxonil CRM certified by a combination of freezing point depression method and 1 H qNMR. For each sample, 1 H qNMR experiments were optimized before quantitative analysis. The results showed that the measured values of each sample were equivalent to the corresponding reference labeled value. Furthermore, assessment of these 1 H qNMR data using the normalized error, E n -value, concluded that statistically 1 H qNMR has the competence to obtain the same quantification performance and accuracy as the conventional primary methods of measurement.

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1D/2D-NMR based extensive analyses of the real structure of aldosterone, elucidating the plausible diastereomeric hemiacetal/hemiketal tautomers and a qNMR based method of absolute content determination.

The title compounds, including the parent 3-azido-2H-azirine, were generated by low-temperature photolysis of the corresponding 1,1-diazidoethenes, and characterised not only by trapping reactions, but also by direct detection using NMR and in situ IR spectroscopy.

The synthesis of postulated 2H,6H-1,5-dithiocines from isonitriles and acetylenedicarboxylates or dibenzoylacetylene in the presence of elemental sulfur was repeated. The products do not possess the structure of eight-membered sulfur heterocycles, but isothiazole-3(2H)-thiones were formed instead. This structural corrigendum was confirmed not only by a critical consideration of the 13 C NMR spectroscopic data and by the correction of the MS spectra and the values of the elemental analyses but also by X-ray crystallographic structure determination. Several reaction mechanisms are discussed to explain the generation of the observed isothiazole-3(2H)-thiones.Esters of acetylene dicarboxylic acid and especially dimethyl acetylenedicarboxylate (DMAD) are highly versatile tools for organic chemists. 1-7 These compounds are successfully utilized as dienophiles in Diels-Alder reactions, as dipolarophiles in 1,3-dipolar cycloaddition reactions and also as components in [2+2] or other cycloaddition reactions. Furthermore, they can be used as powerful Michael acceptors, and, in several cases, nucleophilic addition and formation of zwitterions are combined with other addition or (formal) cycloaddition steps to yield a variety of products by multicomponent reactions. 1 As part of our current studies 8 on unusual reactions of acetylenedicarboxylates, we noticed a report 9 of Alizadeh and Hosseinpour on the synthesis of 2H,6H-1,5-dithiocines 3 by treatment of isonitriles 1 with diesters or diketone 2 in the presence of elemental sulfur (Scheme 1). The products 3a-g were isolated as yellow powders in 80-92% yield and characterized by their sharp melting points (in the range of 95-147 °C), IR, 1 H NMR, 13 C NMR and MS data as well as by elemental analyses. The authors explained the formation of 3 by assuming a nucleophilic addition of 1 at the electronpoor C≡C bond of 2 to generate dipole 4, which attacks sulfur to produce intermediate 5. Dimerization of this species should lead to dithiocine 3. Scheme 1 Claimed 9 and now revised structures of the products resulting from the reaction of 1 with 2 in the presence of elemental sulfur R 1 NC +