B. S. Kikot

Study of the structures of indazoles, pyrazolo [3,4-b] pyridines, and pyrazolo[3,4-b]pyrazine by IR spectroscopy

It is shown on the basis of a study of the IR spectra of indazoles, pyrazolopyridines, and pyrazolopyrazine in the solid state and of their N-deutero-substituted derivatives and hydrochlorides at room temperature and at the temperature of liquid nitrogen that these heterocycles exist in a tautomeric form in which the labile hydrogen atom is localized on the nitrogen atom of the pyrazole ring. It was established that 6-aminopyrazolopyridine exists in the crystalline state in the amino form and that it is protonated at the ring nitrogen atom rather than at the amino group. The applicability of the temperature-shift method for the detection not only of γNH bands but also of γND bands is demonstrated.

IR spectra of diastereomeric (with respect to phosphorus) 2′, 3′-O-alkylphosphonates of nucleosides

In a study of the IR absorption spectra of diastereomeric (with respect to phosphorus) 2′,3′-O-alkylphosphonates of nucleosides it was shown that the IR spectra of the diastereomers differ at 820–860 (ΝO-P-O), 1040–1060 (ΝP-O-C), and 1250–1300 cm−1 (ΝP=O). Higher ΝO=P and ΝP-O-C values and lower ΝO-P-O values are observed for the R isomers (as compared with the S isomers), and this provides a possibility for the determination of the orientation of the P=O group relative to the protons of the phospholane ring in alkylphosphonates of nucleosides by comparison of the spectra of the diastereomers.