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

Two independent mol­ecules comprise the crystallographic asymmetric unit in the title anti­retroviral agent Efavirenz, C14H9ClF3NO2, and these have noteworthy differences in conformation. The major difference relates to the orientation of the 2-cyclo­propyl­ethynyl residue relative to the six-membered heterocycle: this approaches an orthogonal disposition in mol­ecule a compared to a more flattened conformation in mol­ecule b, the difference being reflected in the Oring—C—C—Cethyne torsion angles of 65 (4) and 159 (5)°, respectively. The independent mol­ecules are connected via the eight-membered {⋯HNC (O)}2 amide synthon. Disorder is noted in the cyclo­propane ring of mol­ecule b in that two orientations of equal weight were discerned.