The visible absorbance maximum of 2-hydroxy-1,4-naphthoquinone as a novel probe for the hydrogen bond donor abilities of solvents and solvent mixtures

Autor: Hassan Sedaira, S.A. Soliman, Magda S. Saleh, K. A. Idriss, Elham Y. Hashem
Rok vydání: 1996
Předmět:
Zdroj: Monatshefte f�r Chemie Chemical Monthly. 127:29-42
ISSN: 1434-4475
0026-9247
DOI: 10.1007/bf00807406
Popis: The electronic absorption spectra of 2-hydroxy-1,4-naphthoquinone (HNQ) in one- and two-component solvents are discussed. The visible absorption of this reagent has been shown to arise from a charge-transfer transition of the zwitterionic tautomer stabilized by a hydrogen bond donating solvent. The formation constant of the 1:1 hydrogen bonded complex with methanol, ethanol, andn-propanol has been determined at 25 °C from the spectral behaviour in mixed solvents. The tautomerization equilibrium ofHNQ in aqueous ethanol is demonstrated and characterized. The dependence of the absorbance maximum ofHNQ on the hydrogen bond donor ability of the solvent in the visible spectrum, as measured by theTaft-Kamlet α parameter, has been established. Experimentally derived evidence is supplied to justify the recommendation ofHNQ as a novel probe for hydrogen bond donor ability in pure solvents and in mixed aqueous solvents.
Databáze: OpenAIRE
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