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A study on protonation equilibria in a series of amino‐1‐(substituted phenyl)pyrazoles
Author(s) -
Garrone A.,
Tironi C.,
Fruttero R.,
Gasco A.
Publication year - 1989
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570260601
Subject(s) - chemistry , protonation , substituent , pyrazole , ring (chemistry) , medicinal chemistry , proton , spectral line , ionization , proton affinity , stereochemistry , computational chemistry , organic chemistry , ion , physics , quantum mechanics , astronomy
The ionization constants (proton gain) of 3‐,4‐, and 5‐amino‐1‐(substituted phenyl)pyrazoles, have been measured in 10% v/v ethanol‐water. p K a values show a good linear dependence on Hammett substituent constants. The reaction constants Q are in keeping with the respective protonation sites in the three series of monocations. The uv spectra of 1‐( m ‐nitrophenyl)pyrazole and 1‐( p ‐methoxyphenyl)pyrazole and of their 3‐amino, 4‐amino, 5‐amino analogues recorded in acidic and neutral media, show that in the three series the first protonation site does not change with change in substituent at phenyl ring.