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

Abstract

The title compounds, both C8H4F3NO4, 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.

Influence of the Solvent on the Stability of Aminopurine Tautomers and Properties of the Amino Group

“…An interesting example of the influence of intramolecular interactions on the properties of a substituent is when steric or attractive interactions between neighboring groups cause the rotation of one of them. For example, the rotation of the nitro group, as observed in some compounds [ 56 , 57 ], can decrease the strength of the substituent effect by ~45% in the case of 90° rotation [ 58 ].…”