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13 C NMR investigation of tautomeric and acid‐base equilibria of pyrazolone T and three analogs
Author(s) -
Bell Sandra J.,
Mazzola Eugene P.,
Dinovi Michael J.,
Reynolds William F.,
Nielsen Kathy W.
Publication year - 1991
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.5570280318
Subject(s) - tautomer , chemistry , chemical shift , pyrazolone , heteronuclear molecule , base (topology) , carbon 13 nmr , stereochemistry , computational chemistry , medicinal chemistry , nuclear magnetic resonance spectroscopy , mathematical analysis , mathematics
Pyrazolone T and three derivatives have been characterized by 13 C and, in part, 15 N nmr at several p H values. The 13 C chemical shifts have been assigned at, or near, the equivalence points and p K a values of these four compounds. Closely situatued quaternary carbon signals were assigned by means of a heteronuclear chemical shift correlation (FLOCK) experiment which is sensitive to, and was optimized for, 3‐bond C‐H couplings. The 13 C chemical shift data indicate the existence of both tautomeric and acid‐base equilibria and demonstrate that the four congeners exist in surprisingly different forms at certain common p H values.
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