Alkoxy-benzoic acids: Some lacking structures and rationalization of the molecular features governing their crystalline architectures

• The crystalline structures of four selected (alkoxy)benzoic acids have been solved.
• Trends along the whole set of known structures of such compounds were analyzed.
• Dimeric synthons organize either in parallel or perpendicular architectures.
• The influence of molecular features driving to one or the other was established.
• A specific aromatic C–H⋯π interaction plays a major role.

The crystalline structure of four alkoxy-substituted benzoic acids, namely 3-(methoxy)benzoic acid (I), (with two independent molecules in the asymmetric unit); 3,4-di(ethoxy)benzoic acid (II), 3,5-di(ethoxy)benzoic acid (III) and 3,4,5-tri(ethoxy)benzoic acid (IV) are presented, and the details of their packing arrangements discussed. In all cases the synthon is a H-bonded head-to-head dimer. C–H⋯π interactions involving C atoms at the 4-positions of neighbouring molecules organize the dimeric synthons in a perpendicular orientation in the case of I. These interactions being blocked for II, Van der Waals interchain interactions organise synthons therein in parallel orientation. In the case of III, although C–H⋯π interactions at the 4-positions are possible in principle, interchain interactions prevail, giving rise to a parallel arrangement of linear strands. Finally, compound IV with all three 3,4,5 substituted sites reduces its interaction scheme to stacking contacts, and the columns thus formed are essentially non interacting. An attempt to rationalize the molecular factors influencing the structures of the whole set of 3-, 4- and/or 5-methoxy- and ethoxy-substituted benzoic acids reported so far in the literature is performed.

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