3-[5-(4-Chloro-phen-yl)-1-(4-methoxy-phen-yl)-1H-pyrazol-3-yl]propionic acid and the corresponding methyl ester

The synthesis of 3-[5-(4-chloro-phen-yl)-1-(4-methoxy-phen-yl)-1H-pyrazol- 3-yl]propionic acid, C19H17ClN2O3, (I), and its corresponding methyl ester, methyl 3-[5-(4-chloro-phen-yl)-1-(4-methoxy-phen-yl)-1H-pyrazol-3-yl]propionate, C20H19ClN2O3, (II), is regiospecific. However, correct identification of the regioisomer formed by spectroscopic techniques is not trivial and single-crystal X-ray analysis provided the only means of unambiguous structure determination. Compound (I) crystallizes with Z′ = 2. The propionic acid groups of the two crystallographically unique mol-ecules form a hydrogen-bonded dimer, as is typical of carboxylic acid groups in the solid state. Conformational differences between the meth-oxy-benzene and pyrazole rings give rise to two unique mol-ecules. The structure of (II) features just one mol-ecule in the asymmetric unit and the crystal packing makes greater use than (I) of weak C - H⋯A inter-actions, despite the lack of any functional groups for classical hydrogen bonding.