Infra-red spectra of substituted pyrazolones and some reflexions on the hydrogen bonding

The infra-red spectra of a number of crystalline pyrazol-5-ones with simple alkyl or phenyl substitution in the pyrazolone ring have been measured in the regions of O-H, N-H and double bond stretching-vibrations. The compounds do not show absorption in the C:O stretching-vibration region, provided a...

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Bibliographic Details
Published in:Spectrochimica acta 1961, Vol.17 (1), p.40-50
Main Author: Refn, Susanne
Format: Article
Language:English
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Summary:The infra-red spectra of a number of crystalline pyrazol-5-ones with simple alkyl or phenyl substitution in the pyrazolone ring have been measured in the regions of O-H, N-H and double bond stretching-vibrations. The compounds do not show absorption in the C:O stretching-vibration region, provided an aromatic structure is not excluded by the substitution. The infra-red spectra show that for the pyrazolones with an aromatic character there is a tautomeric equilibrium between two structures, the hydroxy pyrazole and the zwitterion of the corresponding amide-form, and that the molecules are associated through strong intermolecular hydrogen bonds. The information gained from the infra-red spectra on the position of the proton in the hydrogen bond in two cases has been related to the tautomeric equilibrium constants [ K t = (NH form)/(OH form)] estimated from the basic ionization constants.
ISSN:0371-1951
1873-3816
DOI:10.1016/0371-1951(61)80009-X