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How aromatic fluorination exchanges the interaction role of pyridine with carbonyl compounds: The formaldehyde adduct López Alonso, Juan Carlos Macario Farto, Alberto Maris, Assimo Alkorta, Ibon Blanco Rodríguez, Susana Aromatic fluorination Pyridine Carbonyl compounds Pentafluoropyridine Formaldehyde 23 Química Producción Científica The rotational spectrum of the weakly bound complex pentafluoropyridineꞏꞏꞏformaldehyde 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 pairꞏꞏꞏπ-hole interaction, reinforced by a weak C-HꞏꞏꞏN interaction, indicates an exchange of the electron-acceptor roles of both molecules when compared to the pyridineꞏꞏꞏformaldehyde 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 pairꞏꞏꞏπ-hole and π ꞏꞏꞏπ staking interactions. Ministerio de Economía y Competitividad (grant CTQ2016-75253-P) Ministerio de Ciencia, Innovación y Universidades de España (project PGC2018-094644-B-C22) Comunidad Autónoma de Madrid (grant P2018 / EMT-4329 AIRTEC-CM) 2021-10-11T09:30:24Z 2021-10-11T09:30:24Z 2021 info:eu-repo/semantics/article info:eu-repo/semantics/publishedVersion Chemistry – A European Journal, 2021, vol. 27, n. 55, p.13870 –13878 0947-6539 https://uvadoc.uva.es/handle/10324/48998 10.1002/chem.202102163 13870 55 13878 Chemistry – A European Journal 27 1521-3765 eng https://chemistry-europe.onlinelibrary.wiley.com/doi/10.1002/chem.202102163 Attribution-NonCommercial-NoDerivatives 4.0 Internacional info:eu-repo/semantics/openAccess http://creativecommons.org/licenses/by-nc-nd/4.0/ © 2021 The Authors application/pdf Wiley https://uvadoc.uva.es/bitstream/10324/48998/4/How-aromatic-fluorination-exchanges.pdf.jpg Hispana TEXT http://creativecommons.org/licenses/by-nc-nd/4.0/ UVaDOC. Repositorio Documental de la Universidad de Valladolid https://uvadoc.uva.es/handle/10324/48998