Crystallographic and spectroscopic character­ization of 4-nitro-2-(tri­fluoro­meth­yl)benzoic acid and 4-nitro-3-(tri­fluoro­meth­yl)benzoic acid

The title compounds, both C(8)H(4)F(3)NO(4), represent two isomers of nitro tri­fluoro­methyl benzoic acid. The compounds each contain a nitro functionality para to the carb­oxy­lic acid group, with the tri­fluoro­methyl substituent ortho to the acid group in the 2-isomer and ortho to the nitro group in the 3-isomer. The regiochemistry with respect to the tri­fluoro­methyl group results in steric inter­actions that rotate the carb­oxy­lic acid group or the nitro group out of the aromatic plane in the 2- and 3-isomer, respectively. Each mol­ecule engages in inter­molecular hydrogen bonding, forming head-to-tail dimers with graph-set notation R (2) (2)(8) and donor–acceptor hydrogen-bonding distances of 2.7042 (14) Å in the 2-isomer and 2.6337 (16) in the 3-isomer. Recrystallization attempts did not yield untwinned crystals.