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

C.D. ALCÍVAR LEÓN; G. A. ECHEVERRÍA; O.E. PIRO; S.E. ULIC; J.L. JIOS; M. BURGOS PACI; G. A ARGÜELLO

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 fluorescence spectroscopy with the assistance of theoreticalcalculations. The crystal structure of 2 shows chlorine and bromine atoms of the ?CF2Cland ?CH2Br groups on the same side of the molecular plane, while in the most stableconformer predicted by theoretical calculations, these halogen atoms are opposite. Thesedifferences were interpreted in terms of intra- and intermolecular interactions in the crystalpacking. Particularly, the weak non covalent halogen-halogen contact plays a decisive rolein the preferred conformation adopted in solid phase. In addition results of fluorescencespectroscopy are in accordance with the X-ray spectroscopy, since the proposedassociation due to intermolecular interactions was also found in solution, when theconcentration of 2 was increased.