Ethyl group, proton magnetic resonance

Ethyl chloroformate obtained from Aldrich Chemical Company, Inc., was distilled, b.p. 93°. The progress of the reaction may be followed by proton magnetic resonance spectroscopy. Aliquots are partitioned between dichloromethane and water, the organic layer is concentrated, and the spectrum is recorded. A quartet from the ethoxy group of the mixed anhydride appears at 8 4.2. Ethyl chloroformate, which exhibits a quartet at 6 4.3, is removed in the concentration step. 

It has also been possible to confirm the presence of the reduction product of a Schiff base on the polymer by proton magnetic resonance. For this purpose we have used unmodified poly(ethylenimine), since it too catalyzes the decarboxylation of oxalacetate to its product, pyruvate. Unmodified polyethylenimine was mixed with oxalacetate-4-ethyl ester. One-half of this solution was treated with NaBH4 the second half was exposed to a similar environment but no NaBH4 was added. The borohydride-treated polymer exhibited a strong triplet in the nmr spectrum centered at 3.4 ppm upfield from the HOD resonance. This new feature would be expected from the terminal methyl protons of the oxalacetate ester attached to the polymer. Only a very weak triplet was found in the control sample not treated with borohydride. These observations are strong evidence for the formation of Schiff bases with the polymer primary amine groups. Evidently the mechanistic pathway for decarboxylation by the polymer catalyst is similar to that used enzymatically. 

The sulfone group exhibits typical infrared frequencies at 1150 to 1170 and 1330 to 1350 cm"1 (350, 354). Nuclear magnetic resonance spectra have been recorded in acetone for 2- and 5-ethylsulfonylthiazoles and compared to other groups (270). The sulfonyl ethyl substituent induces a general downfield shift compared to the parent sulfides. Prot°ns in the 2-and 4-positions appear at 9.42 and 8.45 ppm. respectively, in 5-ethvlsulfonylthiazole and the protons at both the 4- and 5-positions emerge at 8.15 ppm in 2-ethylsulfonylthiazole. 

NMR spectrum of the same ethyl alcohol molecules is given in Figure 8.9b measured by a high-resolution NMR spectrometer. It can be seen that the proton resonance of the different functional groups CH3, CH2 and OH takes place at different values of the magnetic field (on account of the difference in g). There follows, in particular, an important conclusion that the number of NMR signals on the spectrum is equal to the number of structure-nonequivalent protons in the molecule. (For instance, in benzene there will be one signal, in mono-substituted benzene there will be three, in ortho-di-fluorine-benzene—one, in para-di-fluorine-benzine—one, in meta-di-fluorine-benzine—two, etc). 

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