How Aromatic Fluorination Exchanges the Interaction Role of Pyridine with Carbonyl Compounds: The Formaldehyde Adduct |
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Authors: | Prof. Juan Carlos López Dr. Alberto Macario Prof. Assimo Maris Prof. Ibon Alkorta Prof. Susana Blanco |
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Affiliation: | 1. Departamento de Química Física y Química Inorgánica, Facultad de Ciencias, IU CINQUIMA, Universidad de Valladolid, 47011 Valladolid, Spain;2. Dipartimento di Chimica “G. Ciamician”, Università di Bologna, Via Selmi 2, I-40126 Bologna, Italy;3. Instituto de Química Médica (CSIC), Juan de la Cierva 3, 28006 Madrid, Spain |
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Abstract: | The rotational spectrum of the weakly bound complex pentafluoropyridine⋅⋅⋅formaldehyde has been investigated using Fourier transform microwave spectroscopy. From the analysis of the rotational parameters of the parent species and of the 13C and 15N isotopologues, the structural arrangement of the adduct has been unambiguously established. The full ring fluorination of pyridine has a dramatic effect on its binding properties: It alters the electron density distribution at the π-cloud of pyridine creating a π-hole and changing its electron donor-acceptor capabilities. In the complex, formaldehyde lies above the aromatic ring with one of the oxygen lone pairs, as conventionally envisaged, pointing toward its centre. This lone pair⋅⋅⋅π-hole interaction, reinforced by a weak C−H⋅⋅⋅N interaction, indicates an exchange of the electron-acceptor roles of both molecules when compared to the pyridine⋅⋅⋅formaldehyde adduct. Tunnelling doublets due to the internal rotation of formaldehyde have also been observed and analysed leading to a discussion on the competition between lone pair⋅⋅⋅π-hole and π⋅⋅⋅π stacking interactions. |
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Keywords: | fluorine molecular adducts non-covalent interactions pi-hole interactions rotational spectroscopy |
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