Investigations on 1-azabicycles. 26*. IR spectra of the simplest pyrrolizidine alcohols in the region of the stretching vibrations of the hydroxyl group and their connection with the stereochemistry of the compounds

Abstract

The IR spectra in the hydroxyl group stretching vibration region of the simplest hydroxyalkylpyrrolizidines have been examined. The spectra were taken in the form of pure liquids, dilute solutions in carbon tetrachloride, and for individual bases in the gas phase. It was shown that in dilute solutions ∆ν OH depends on the geometric parameters of the intramolecular hydrogen bond (IMHB) . The energy of the IMHB of 3-(2-hydroxyethyl)pyrrolizidine was measured in dilute solution and in the gas phase.A large number of studies has been devoted to the synthesis and structure of pyrrolizidine alcohols, especially those forming the basis of pyrrolizidine alkaloids. In spite of this, problems linked with hydrogen bonds in pyrrolizidine alcohols have obtained only limited exposure. The investigation of aminodiols, the alkaloids platinecine and retronecine, in which the hydroxyl groups are connected with hydrogen bonds, are part of the previous work in this region [2].Meanwhile, regularities of the link of the structure of compounds with the character of the absorption in the region of stretching vibrations of the OH group, found for the simplest pyrrolizidine alcohols, are of interest not only in themselves but may also prove to be useful when investigating more complex compounds of this series.

Pyrrolizidine alkaloids

“…A third paper 4 discusses the IR spectra (O-H stretching frequency) of simple pyrrolizidine alcohols, connecting these data to stereochemistry. Again, trends were ascribed to the presence and extent of intra-or intermolecular hydrogen bonding and interactions with the solvent.…”