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Conformational equilibria in o-anisic acid and its monohydrated complex: the prevalence of the trans-COOH form
Juan Carlos López1, Alberto Macario, Susana Blanco
1Departamento de Química Física y Química Inorgánica, Facultad de Ciencias, Universidad de Valladolid, 47011 Valladolid, Spain. jclopez@qf.uva.es sblanco@qf.uva.es.
Abstract:
The conformation of ortho-anisic acid and its monohydrated clusters generated in a supersonic jet has been studied by rotational spectroscopy to analyze the structural implications of ortho substitution. The dominant monomer species shows a trans-COOH arrangement stabilized by an intramolecular O-HO hydrogen bond from the acid to the methoxy group. The spectra of two non-planar skeleton monomer forms with a cis-COOH arrangement have also been detected. A tunneling doublet has been observed for the most stable cis-COOH conformer. The periodic potential energy function for the COOH internal rotation connecting these cis forms has been estimated from the experimental data. For the first time a water complex with an acid in a trans-COOH configuration has been observed. This is more abundant than the other weak form observed for the complex, characterized by a cis-COOH arrangement. The observation of the rotational spectra of salicylic acid, methyl salicylate and methyl 2-methoxybenzoate, formed upon heating of ortho-anisic acid, gives additional interest in the chemistry of ortho substituted benzoic acids.
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