Infrared spectra, hydrogen-bonded

Figure 12.15 The four regions of the infrared spectrum single bonds to hydrogen, triple bonds, double bonds, and fingerprint.

Hydroxypyridine 1-oxide is insoluble in chloroform and other suitable solvents, and, although the solid-state infrared spectrum indicates that strong intermolecular hydrogen bonding occurs, no additional structural conclusions could be reached. Jaffe has attempted to deduce the structure of 4-hydroxypyridine 1-oxide using the Hammett equation and molecular orbital calculations. This tautomeric compound reacts with diazomethane to give both the 1- and 4-methoxy derivatives, " and the relation of its structure to other chemical reactions has been discussed by Hayashi. ... 

The tautomeric behavior of compounds of type 59 has been discussed by Meyer and Vaughan. An intramolecularly hydrogen-bonded 0X0 structure has been assigned to 60 on the basis of its infrared spectrum," whereas unambiguous chemical evidence, i.e., ozo-nolysis to succimide, confirmed the isolation of 61 in the oxo form. The foregoing results may be summarized as follows potential a-hydroxypyrroles exist as pyrrolones. Substituents in the 3-position and in the 5-position favor the A and the A -pyrrolone structure, respectively, as is to be expected. For 3,4,5-trisubstituted compounds, such as 61b, the A -sti ucturc appears to be preferred. An electron-... 

Another objection to Pauling s model is that it would include hydrogen bonds of different kinds which should show up in the infrared spectrum but for which there is so far no evidence. 

Figure 3. Hydrogen and oxygen velocity autocorrelation function from two-body MCY with vibrations allowed (MCYL), and computed infrared spectrum for intramolecular bending modes and bond stretching.

First use the molecular formula and the equation given above to calculate the number of double bond equivalents. In this case (remembering to treat bromine as equivalent to hydrogen) the value is 1. The infrared spectrum shows a band at 1641 cm 1, which probably represents the C=C bond stretch, but in this case there can only be a C=C bond present ... 

The infrared spectrum of erythromycin is commonly used for its identification. Figure 2 shows the spectrum of a 75 mg./ml. chloroform solution. The bands at 1685 and 1730 cm- are due to the ketone carbonyl and the lactone carbonyl, respectively. The absorption peaks between 1000 and 1200 cm-1 are due to the ethers and amine functions. The CH2 bending is evidenced by peaks between 1340 and 1460 cm-, and alkane stretching peaks appear between 2780 and 3020 cm-. Hydrogen bonded OH and water appear as bands between 3400 and 3700 cm-1. 

Figure 14.4. Infrared spectra showing common absorption bands. The —OH of acids and alcohols are hydrogen-bonded, leading to broadening.The —OH of hexanoic acid, which is unusually sharp, absorbs in the 3500-2500 cm-1 region. Bottom spectrum shows absorptions due to functional groups in the compounds making up the mixture.

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