Crystal structure and Hirshfeld-surface analysis of an etoxazole metabolite designated R13

The etoxazole metabolite R13, systematic name 4-(4-tert-butyl-2-eth-oxy-phen-yl)-2-(2,6-di-fluoro-phen-yl)oxazole (C₂₁H₂₁F₂NO₂), results from the oxidation of etoxazole, a chitin synthesis inhibitor belonging to the oxazoline class, widely used as an insecticide/acaricide since 1998. The structure of R13 features a central oxazole ring with attached 2,6-di-fluoro-phenyl and 4-t-butyl-2-eth-oxy-phenyl moieties. The overall conformation gives dihedral angles between these rings and the oxazole of 24.91 (5)° (with di-fluoro-phen-yl) and 15.30 (6)° (with t-butyl-eth-oxy-phen-yl), indicating an overall deviation from planarity. Additionally, torsion angles of the eth-oxy and t-butyl groups define the orientation of these substituents relative to their benzene ring. In the crystal packing, no significant hydrogen bonds are present, but a Hirshfeld surface analysis highlights weak inter-molecular contacts leading to π-π-stacked dimers linked by weak C-H⋯N contacts. The packing analysis confirms that most inter-molecular inter-actions involve hydrogen atoms.