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How Aromatic Fluorination Exchanges the Interaction Role of Pyridine with Carbonyl Compounds: The Formaldehyde Adduct
Author(s) -
López Juan Carlos,
Macario Alberto,
Maris Assimo,
Alkorta Ibon,
Blanco Susana
Publication year - 2021
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202102163
Subject(s) - lone pair , pyridine , adduct , chemistry , isotopologue , formaldehyde , stacking , ring (chemistry) , acceptor , rotational spectroscopy , photochemistry , crystallography , molecule , computational chemistry , medicinal chemistry , organic chemistry , physics , condensed matter physics
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 13 C and 15 N 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.