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4‐Hydroxycoumarin/2‐hydroxychromone tautomerism: Infrared spectra of 2‐ 13 c and 3‐D labeled 4‐hydroxycoumarin and its anion
Author(s) -
Obaseki Andrew O.,
Porter William R.,
Trager William F.
Publication year - 1982
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.5570190234
Subject(s) - chemistry , delocalized electron , tautomer , ion , infrared spectroscopy , anhydrous , 4 hydroxycoumarin , deuterium , crystallography , photochemistry , medicinal chemistry , analytical chemistry (journal) , organic chemistry , physics , catalysis , quantum mechanics
Bands with primarily v (C=O) and v (C=O) character in the spectra of 4‐hydroxycoumarin and its anion were identified by isotopic substitution with either 13 C or deuterium. Two bands of each type were found for spectra of 4‐hydroxycoumarin in solution in chloroform, dioxane, or dimethylsulfoxide, with v (C=O) at 1704–1733 cm −1 and ∼ 1567 cm −1 . Two bands, at 1618 and 1559 cm −1 , are associated with v (C=C) in the spectrum of crystalline 4‐hydroxycoumarin monohydrate, but only a single v (C=O) band at ∼ 1655 cm −1 was observed. Anhydrous 4‐hydroxycoumarin has v (C=O) bands at ∼ 1700 cm −1 and a shoulder at ∼ 1670 cm −1 . The strong band at 1660 cm −1 in the spectrum of 4‐hydroxycommarin anion in dimethylsulfoxide solution is due to a delocalized v (O = C = O) vibration, whereas the band at 1555 cm −1 has partial v (C=C) character and involves C(3) but not C(2), supporting a fully delocalized char structure for the anion. No evidence for the existence of the 2‐hydroxychromone tautomer was found, except in the case of anhydrous 4‐hydroxycoumarin in the solid state.