“Infrared Spectra of Steroids. II. The Influence of the Solvent on Carbonyl Frequency Correlations”

Abstract

The influence of solvents on frequencies of the carbonyl absorption bands in the infrared spectra of 56 steroids has been investigated with a double beam spectrophotometer. Good agreement was obtained with data previously published for the characteristic frequencies in carbon disulfide for similar types of ketosteroids. The carbonyl absorption maxima in chloroform and methylene bromide were displaced toward lower frequencies by about 2–17 cm⁻¹ from their frequencies in carbon disulfide or carbon tetrachloride. The magnitude of the shift depended upon the location and type of carbonyl group. Additional dispalcement of the order of 1–19 cm⁻¹ was found in bromoform solution. In mineral oil spectra, considerable variation in frequencies were observed for a particular carbonyl group at the same position in different steroid molecules. The absorption maxima of two Δ⁵-7-ketosteroids are reported for the first time to be at the same position as those of Δ⁴-3-ketosteroids. A new interaction of the 3 a, 9a-epoxides with the 11 carbonyl group has been suggested. While Δ⁴-3-ketosteroids could not be distinguished from Δ⁹-12-ketosteroids in carbon disulfide or carbon tetrachloride, the absorption maxima were at sufficiently different frequencies in chloroform or methylene bromide. In a series of four ketones with the carbonyl group at different positions along the side chain, it was observed that the 24 and 25 carbonyl absorption bands were closer to those of simple aliphatic ketones than the 20 and 22 ketones. A similar shift to higher frequencies as the chain length was increased was observed for three steroid acids. When the ketonic absorption band was very close to that of an acetate, broadening of the latter band in chloroform, methylene bromide and bromoform resulted in poor resolution.