Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 2008-12-01

Charge transfer interaction of 4-acetamidophenol (paracetamol) with 2,3-dichloro-1,4-naphthoquinone: a study in aqueous ethanol medium by UV-vis spectroscopic and DFT methods.

Avijit Saha, Amit S Tiwary, Asok K Mukherjee

Index: Spectrochim. Acta. A. Mol. Biomol. Spectrosc. 71(3) , 835-40, (2008)

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Abstract

4-Acetamidophenol (paracetamol) is shown to form charge transfer complex with 2,3-dichloro1,4-naphthoquinone in aqueous ethanol media exhibiting the unusual 2:1 (paracetamol:quinone) stoichiometry. The complexation enthalpy and entropy have been estimated from the formation constant (K) determined spectrophotometrically at five different temperatures. In aqueous ethanol mixtures of varying composition K increases with increasing dielectric constant of the medium. This has been rationalized by calculating the electronic charge distribution in paracetamol molecule and its conjugate base at the DFT/B3LYP/6-31++G(d,p) level. The theoretically calculated vertical ionization potential of paracetamol also agrees with reported experimental value.