The role of halogen C?X1---X2?C contact on the preferred conformation of 2-perhalomethylchromones in solid state

ECHEVERRÍA G. A.; JORGE L. JIOS; ALCÍVAR LEÓN; JULIAN FEW; GUSTAVO A ARGÜELLO; PIRO O. E. ; MAXI A. BURGOS PACI

CHEMICAL PHYSICS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2016 vol. 472 p. 142 - 155

0301-0104

The solid state of 2-chlorodifluoromethyl-3-methylchromone (1) and 3-bromomethyl-2-chlorodifluoromethylchromone(2) was studied by vibrational spectroscopy (IR, Raman) and X-ray diffraction methods.The analysis was extended to solution phase using UV?Vis, NMR (1H, 13C and 19F) and fluorescencespectroscopy with the assistance of theoretical calculations. The crystal structure of 2 shows chlorine andbromine atoms of the ?CF2Cl and ?CH2Br groups on the same side of the molecular plane, while in themost stable conformer predicted by theoretical calculations, these halogen atoms are opposite. These differenceswere interpreted in terms of intra- and intermolecular interactions in the crystal packing.Particularly, the weak non covalent halogen?halogen contact plays a decisive role in the preferred conformationadopted in solid phase. In addition, results of fluorescence spectroscopy are in accordance withthe X-ray spectroscopy, since the proposed association due to intermolecular interactions was also foundin solution when the concentration of 2 was increased.