NMR spectroscopy Water

Hinedi, Z. R., Chang, A. C., and Borchardt, D. B. (1997). Probing the association of fluorobenzene with dissolved organic matter using NMR spectroscopy. Water Res. 31, 877-883. 

The concentrations of the different intermediates are determined by the equilibrium constants. The observation of immonium ions [Eq. (5)] in strongly acidic solutions by ultraviolet and NMR spectroscopy also Indicates that these equilibria really exist (23,26). The equilibria in aqueous solutions are of synthetic interest and explain the convenient method for the preparation of 2-deuterated ketones and aldehydes by hydrolysis of enamines in heavy water (27). 

Tlie IR and and NMR spectra for thiazolo[5,4-h]quinolines 86 demonstrate their existence in the hydroxy form (96T11929). Tlie preference for IH,6H tautomer 87a in water and in the solid state is supported by and NMR spectroscopy, ab initio (STO-3G ) and X-ray crystallographic studies [75AX(B)1427 92H1399]. 

A solution of 1.0 g (33 mmol) of the mixture of heptofuranoside diastereomers (14) in 5 ntL of THE is stirred in an ice-water bath. 3.4 mL of 1 M soln ofTBAF (3.4 mmol) in THF are added, and Ihe reaction is monitored by TLC (CHCI,/CH, OH, 9 1). After ca. 15 min, the reaction mixture is carefully neutralized with dil sulfuric acid, then diluted with water and extracted with CHC13. The extract is dried over Na,S04 and concentrated to give an off-white solid which is a single stereoisomer (by NMR spectroscopy). Column chromatography gives the inositol as a white solid yield 0.61 g (70%) mp 186-187 C (benzene/CH,OH) [a]D + 118 (c = 03, CH, OH). 

In a 70 ml culture tube equipped with a Teflon lined cap, 10 ml 0.2 M 7 was mixed with 10 ml 1 M Me3Al in CH2C12 solvent at 22 °C in a dry box under nitrogen atmosphere. After one hour the Me3Al was destroyed by slowly adding methanol to the mixture. The tube was withdrawn from the dry box, and the reaction mixture was washed with ice-cold 0.5 N HC1 solution and water, separated, dried over anhydrous MgS04, solvent was evaporated under vacuum, and the products were analyzed by H1 NMR spectroscopy. 

However, we have to criticize more specifically the paper by Lown et al. (1984), who characterized alkanediazonium ions, as well as (E)- and (Z)-alkanediazoate ions, by 15N NMR spectroscopy. They also report NMR data on the (E)- and (Z)-benzenediazohydroxides as reference compounds, describing the way they obtained these compounds in only three lines. Obviously the authors are not familiar with the work on the complex system of acid-base equilibria which led 30 years earlier to the conclusion that the maximum equilibrium concentration of benzenediazohydroxide is less than 1 % of the stoichiometric concentration in water (see Ch. 5). The method of Lown et al. consists in adding 10% (v/v) water to a mixture of benzenediazonium chloride and KOH in dimethylsulfoxide. In the opinion of the present author it is unlikely that this procedure yields the (Z)- and CE>benzenediazohydroxides. Such a claim needs more detailed experimental evidence. 

The incorporation of water in the structure of cellulose influences. Upon the hydrogen bond structure of the macromolecule. A great deal of work has been done in this area. Calorimetric methods have been invaluable in helping to solve the problem 23 It is, however evident that solid-state NMR spectroscopy may also give valuable information. 

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