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Published on: April 28, 2023
Molecular Structure and Internal Dynamics of 2'-Hydroxyacetophenone by Free-Jet Absorption Millimeter-Wave
Salvatore Boi1, Sonia Melandri1,2,3, Luca Evangelisti2,3,4
1Department of Chemistry G. Ciamician, University of Bologna, 40126 Bologna, Italy.
Abstract:
The rotational spectrum of 2'-hydroxyacetophenone has been recorded and assigned for the first time using a Stark-modulated free-jet absorption millimeter-wave (FJ-AMMW) spectrometer in the 59.6-74.5 GHz frequency range. The most stable conformer has been detected and assigned: A = 2277.076(11), B = 1212.113(5) and C = 795.278(5) MHz. It is characterized by a Cs symmetry where a strong hydrogen bond between the acetyl oxygen atom and the hydroxyl atom takes place. The transition lines show a fine structure due to the internal rotation of the methyl group, which allowed the determination of a V3 = 565.1(5) cm-1 barrier. The corresponding tunneling splittings have been estimated to be 51 MHz. Calculations at the B3LYP-D3(BJ)/Def2-TZVP level underestimate the height of the barrier by about 156 cm-1. This value decreases to 25 cm-1 with MP2/aug-cc-pVTZ.
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However, the stretching absorptions for the C=O bond vary depending on the structure of carboxylic acids. The C=O bond of the free carboxylic acids shows a higher stretching frequency, 1760 cm−1, while H-bonded carboxylic acids (dimers) exhibit stretching absorptions at a lower frequency,...

