Structural hydroxyl groups, infrared spectra

These structural problems are also insoluble by physical methods alone. The infrared spectrum often gives an unambiguous decision about the structure in the solid state the characteristic bands of the carbonyl or the hydroxyl group decided whether the compound in question is a carbinolamine or an amino-aldehyde. However, tautomeric equilibria occur only in solution or in the liquid or gaseous states. Neither infrared nor ultraviolet spectroscopy are sufficiently sensitive to investigate equilibria in which the concentration of one of the isomers is very small but is still not negligible with respect to the chemical reaction. 

The existence of imidazole-4-aldehyde (232) in the enolic form 233 was postulated on the basis of chemical evidence," but the infrared spectrum indicates the presence of a carbonyl group and absence of a hydroxyl group, suggesting that structure 232 should... 

By comparisons among the spectra of large numbers of compounds of known structure, it lias been possible to recognize, at specific positions in the spectrum, bands which can be identified as characteristic group frequencies associated with the presence of localized units of molecular structure in the molecule, such as methyl, carbonyl, or hydroxyl groups. Many of these group frequencies differ in the Raman and infrared spectra. 

The nature of the acidity of mordenite and its relation to catalytic activity have been investigated by Benesi (757), Lefrancois and Malbois (227) and Eberly et al. (225). Eberly et al. observed two absorption bands in the hydroxyl region of the infrared spectrum of H-mordenite. A band at 3740 cm-1 was attributed to silica-type hydroxyl groups, and a lower frequency band, 3590 cm-1, was thought to arise from hydroxyl groups associated with aluminum atoms in the structure. Acid extraction of the aluminum atoms from the framework, although leaving the structure intact resulted in a loss of the lower frequency hydroxyl band. 

Let ns stay a bit with the example of the spectroscopist. Let ns assume he is a specialist in infrared spectroscopy. One of the features of a structural drawing he wonld pay special attention to is hydroxy groups. The reason he does this is because his experience tells him that hydroxyl groups can usually be seen as a broad band at the beginning of an infrared spectrum. He translates this information almost automatically into a hydroxyl band in the spectrum. 

The study of fine structure in cellulose by infrared spectroscopy rests largely on the ease with which this technique can characterize the hydrogenbonding system of the hydroxyl groups. There are other changes in the spectrum caused by fine-structure changes (see, for example, Section III.2), but some of these are more difficult to interpret and are used in an empirical manner only. 

The chemical structure of baogongteng A (1), a new myotic agent from Erycibe obtusifolia, has been determined. High-resolution mass-spectral data indicated the presence of a 3,6-disubstituted tropane skeleton. Infrared and and n.m.r. data indicated the presence of secondary amine, secondary hydroxyl, and acetoxy functions, and the location of the latter group at C-6 was based on comparison of n.m.r. chemical shifts with those of 6B-acetoxy-3a-tropanol. The hydroxyl group was assigned to the 23-position from the n.m.r. spectrum of the N-methylated alkaloid. 

Polymer from Pentaerythritol and 1,4-Cyclohexanedione, An infrared spectrum of the spiro polymer indicates that this material contains a very small number of hydroxyl groups (3400cm ), which are due either to entrapped starting materials or to end groups on the polymer. For the most part, however, the polymer seems to consist of a polyspiroketal structure since its spectrum is similar to that of pentaerythriol dibutyral. 

Acid hydrolysis of serratamic acid gave a nitrogen-free acid, C10H20O3J and a water soluble component identical with L-serine. The acid, m.p. 47°C, [ajo —19° (chloroform), was identified as 3(d)-hydroxydecanoic acid. As serratamic acid exhibits amide bands in its infrared spectrum (1649, 1632, 1549 cm" ) and contains a primary hydroxyl group, structure (1), N-(3D-hydroxydecanoyl)-L-serine, was proposed (6) (Scheme 1). This structure was confirmed by synthesis from 3d-hydroxydecanoic acid and L-serine methyl ester (7). 

Kopsine. Kopsine is a heptacyclic alkaloid which at first sight would appear to offer little hope of rapid structure elucidation, but the reader should remember how much information can be gotten out of quite simple measurements. The nature of its chromophoric moiety followed from its ultraviolet absorption spectrum the infrared revealed its carbonyl functionalities. From the above, the elemental composition, Zeisel and Kuhn-Roth determinations and behaviour towards hydrogenation it seemed to be a heptacyclic-N-methoxycarbonylindoline containing a keto-carbonyl and a hydroxyl group. 

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