(S)-6-Chloro-4-cyclo­propyl­ethynyl-4-trifluoro­methyl-1H-3,1-benzoxazin-2(4H)-one

Two independent mol-ecules comprise the crystallographic asymmetric unit in the title anti-retroviral agent Efavirenz, C(14)H(9)ClF(3)NO(2), and these have noteworthy differences in conformation. The major difference relates to the orientation of the 2-cyclo-propyl-ethynyl residue relative to the six-membered heterocycle: this approaches an orthogonal disposition in mol-ecule a compared to a more flattened conformation in mol-ecule b, the difference being reflected in the O(ring)-C-C-C(ethyne) torsion angles of 65 (4) and 159 (5)°, respectively. The independent mol-ecules are connected via the eight-membered {⋯HNC (O)}(2) amide synthon. Disorder is noted in the cyclo-propane ring of mol-ecule b in that two orientations of equal weight were discerned.