Esters nuclear magnetic resonance

Nagayama et al. [36] studied a-sulfonation using nuclear magnetic resonance (NMR). They reported the presence of two intermediates. The first intermediate is the adduct of S03 to the carbonyl oxygen formed at low temperatures. In contrast to the mechanism of Stein et al., they did not propose a rearrangement of this intermediate but a second addition of S03 to the activated a-hydrogen to give the second intermediate. The reaction of the intermediate with sodium hydroxide can lead to the disodium salt if the neutralization is immediate or to the sodium a-sulfo fatty acid ester if the neutralization is delayed. 

Nuclear magnetic resonance spectrometry has been used to quantitate aspirin in a combination product with a coefficient of variation of 1.1.102 For quantitation, the shift at 2.3 ppm representing the ester methyl group was used. 

JS Davies, RJ Thomas, MK Williams. Nuclear magnetic resonance spectra of ben-zoyldipeptide esters. A convenient test for racemisation in peptide synthesis. J Chem Soc Chem Commun 76, 1975. 

Residues identified on field-treated kale other than malathion included the oxygen analog and the impurity identified by nuclear magnetic resonance and mass spectrometry as ethyl butyl mercaptosuccinate, 5-ester with 0,0-dimethyl phosphorodithioate. This compound did not form as an alteration product of malathion but was present in the 50% emulsifiable concentrate (Gardner et al, 1969). 

The reaction of few phenols with acetylenic esters is reported in the literature. " George and co-workers, on the basis of detailed nuclear magnetic resonance (NMR) studies of the product mixtures formed in the reaction of several phenols with DMAD, have concluded that, as the size of the attacking nucleophile increases, there is a greater tendency for the formation of maleates, which are sterically more favored as compared to the fumarates. 

The structures of vanicosides A (1) and B (2) and hydropiperoside (3) were established primarily by one- and two-dimensional nuclear magnetic resonance (NMR) spectroscopy techniques and fast atom bombardment (FAB) mass spectrometry (MS).22 The presence of two different types of phenylpropanoid esters in 1 and 2 was established first through the proton (4H) NMR spectra which showed resonances for two different aromatic substitution patterns in the spectrum of each compound. Integration of the aromatic region defined these as three symmetrically substituted phenyl rings, due to three p-coumaryl moieties, and one 1,3,4-trisubstituted phenyl ring, due to a feruloyl ester. The presence of a sucrose backbone was established by two series of coupled protons between 3.2 and 5.7 ppm in the HNMR spectra, particularly the characteristic C-l (anomeric) and C-3 proton doublets... 

Mixtures of isomeric di-ALoxides are generally obtained when 5(6)-substituted benzofurazan 1-oxides (51) are used in the Beirut reaction52-54 however, only 7-substituted 2-cyano-3-phenylquin-oxaline 1,4-dioxides (52) were isolated from benzoylacetonitrile (PhCOCH2CN).55 The di-AAoxide mixtures obtained from reaction with acetonyl methyl sulfide (MeCOCH2SMe) were analyzed by H nuclear magnetic resonance (NMR) analysis of the mixed hydroxamic esters (53) formed by hydrolysis and methylation of the primary products.52... 

Jensen et al43 have confirmed both the stoichiometry of equation (17), and the fourth-order rate expression (18) for the symmetrisation of the tert.-butyl ester of a-carboxybenzylmercuric bromide in a study by nuclear magnetic resonance. The fourth-order rate coefficient remained constant at about 15 x 10-4 l3.mole-3. sec-1 at 31.4 °C over a wide range of initial concentrations of both the mercuric compound and of ammonia. Of mechanisms B and C, these workers preferred C. 

If the unknown, neutral, oxygen-containing compound does not give the class reactions for aldehydes, ketones, esters and anhydrides, it is probably either an alcohol or an ether. Alcohols are readily identified by the intense characteristic hydroxyl adsorption which occurs as a broad band in the infrared spectrum at 3600-3300 cm-1 (O—H str.). In the nuclear magnetic resonance spectrum, the adsorption by the proton in the hydroxyl group gives rise to a broad peak the chemical shift of which is rather variable the peak disappears on deuteration. 

C.A. Glass and H.J. Dutton, Determination of beta-olefinic methyl groups in esters of fatty acids by nuclear magnetic resonance, Anal. Chem. 36 (1964) 2401-2404. 

Computational efforts to describe the conformational preferences of (R,R)-tartaric acid and its derivatives - mainly for isolated molecules - were made recently [18-25]. The conformations of these molecules also attracted attention from experimental chemists [22-40]. (/ ,/ [-tartaric acid and its dimethyl diester were observed in crystals, in conformations with extended carbon chain and planar a-hydroxy-carboxylic moieties (T.v.v and Tas for the acid and the ester, respectively) [25-28] (see Figure 2). The predominance ofthe T-structure was also shown by studies of optical rotation [31], vibrational circular dichroism (VCD) [23], Raman optical activity [32, 35], and nuclear magnetic resonance (NMR) [22, 33, 34]. The results of ab-initio and semiempirical calculations indicated that for the isolated molecules the Tsv and T as conformers were those of lowest energy [22, 21, 23, 25]. It should be noted, however, that early interpretations of NMR and VCD studies indicated that for the dimethyl diester of (/ ,/ [-tartaric acid the G+ conformation is favored [36-38]. 

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