Spectra IRS of Bile Acids

Infrared radiation, i.e., wavelengths from 1 to 100 n (corresponding to the frequency range from about 10,000 to 100 cm ), is absorbed and converted by organic molecules into energy of molecular vibration. Although this absorption is quantitized, the vibrational spectra appear as bands rather 

The band positions associated with the various vibrations are primarily dependent on mass- and force-constant effects. They are sensitive to small, but highly specific perturbations, induced by effect of stereo chemistry, mechanical coupling, intramolecular electrical effects, and intermolecular interaction. Thus, the physical state of the compound, liquid, amorphous solid, crystalline solid (including polymorphism) may alter the frequency of absorption. When using band-by-band correlation with a standard compound for identification of an unknown, these factors should be considered. More detailed information appears in the textbooks on infrared spectroscopy (48-53). 

The spectra of the bile acids are shown in Figs. 7 and 8. Band positions and assignments are given in Table I and spectra are discussed using letters. a through i as indicated in Table I. 

In carboxylic acids with no other proton-accepting or -donating groups present in the molecule or available in a solvent the predominant mode of 

3600-3200 f3000 very broadl 2700 shoulder [ U600 shoulder J 2900 

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