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

BANERJEE, PUJARINI ; BHATTACHARYA, INDRANI ; CHAKRABORTY, TAPAS (2016) Matrix isolation infrared spectra of O-H ⋯ π Hydrogen bonded complexes of Acetic acid and Trifluoroacetic acid with Benzene Journal of Chemical Sciences, 128 (10). pp. 1549-1555. ISSN 0974-3626

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Official URL: http://doi.org/10.1007/s12039-016-1165-2

Related URL: http://dx.doi.org/10.1007/s12039-016-1165-2

Abstract

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 (ν O−H) of the carboxylic acid groups of the two molecules are observed to have almost the same value. However, the spectral red-shifts of ν O−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 (p K a ) in aqueous media. Furthermore, Δν O−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 (Δν O−H) of phenol-Bz and carboxylic acid-Bz complexes show similar dependence on the acidity factor (p K a). 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.

Item Type:Article
Source:Copyright of this article belongs to Springer Nature Switzerland AG
Keywords:Matrix isolation;pi-hydrogen bonding;infrared spectroscopy;spectral shifts;charge transfer.
ID Code:135535
Deposited On:25 Jan 2023 05:21
Last Modified:25 Jan 2023 05:21

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