Articles written in Journal of Chemical Sciences

    • Matrix isolation infrared spectra of O-H· · · π Hydrogen bonded complexes of Acetic acid and Trifluoroacetic acid with Benzene


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      Mid infrared spectra of two O–H· · · π hydrogen-bonded binary complexes of acetic acid (AA) and trifluoroacetic acid (F₃AA) with benzene (Bz) have been measured by isolating the complexes in an argon matrix at ∼8 K. In a matrix isolation condition, the O–H stretching fundamentals (νO−H) of the carboxylic acid groups of the two molecules are observed to have almost the same value. However, the spectral red-shifts of νO−H bands of the two acids on complexation with Bz are largely different, 90 and 150 cm⁻¹ for AA and F₃AA, respectively. Thus, the O–H bond weakening of the two acids upon binding with Bz in a non-interacting environment follows the sequence of their ionic dissociation tendencies (pKa) in aqueous media. Furthermore, ΔνO−H of the latter complex is the largest among the known π-hydrogen bonded binary complexes of prototypical O–H donors reported so far with respect to Bz as acceptor. It is also observed that the spectral shifts (ΔνO−H) of phenol-Bz and carboxylic acid-Bz complexes show similar dependence on the acidity factor (pKa). Electronic structure theory has been used to suggest suitable geometries of the complexes that are consistent with the measured IR spectral changes. Calculation at MP2/6-311++G (d, p) level predicts a T-shaped geometry for both AA-Bz and F₃AA-Bz complexes, and the corresponding binding energies are 3.0 and 4.5 kcal/mol, respectively. Natural Bond Orbital (NBO) analysis has been performed to correlate the observed spectral behavior of the complexes with the electronic structure parameters.

    • Photoisomerization of acetone via Rydberg excitation


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      Acetone photochemistry upon excitation by vacuum ultraviolet (VUV) radiation of photonenergy 7.75 eV has been investigated under a cryogenic condition of an argon matrix (8 K) and also by shining the molecule seeded in an effusive beam of argon prior to matrix deposition on a pre-cooled KBr window, where the photo-products get trapped in the argon matrix. Product analysis by infrared spectroscopy reveals appearance of the characteristic enolic O-H stretching fundamental at 3622 cm-1 and other bands in the infrared fingerprint region, including C=C stretching only in the gas phase. The findings reveal the opening of a new isomerization reaction channel of acetone over the popular Norrish type-I α-CC bond cleavage upon VUV excitation to high-lying Rydberg states.

      SYNOPSIS Photochemical transformation of acetone upon excitation by vacuum ultraviolet radiation of photon energy 7.75 eV is reported under a cryogenic condition of an argon matrix (8 K). Infrared spectroscopic analysis of the products reveals that acetone isomerizes to the enolic form, 1-propene-2-ol, upon excitation to the high-lying Rydberg states.

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