Four Methyl Azolyl-3-propenoates

The structures of four azolyl-3-propenoic esters, methyl (E)-3-(imidazol-4-yl)propenoate, (2), as its hemihydrate, C₇H₈N₂O₂.0.5H₂O, methyl (E)-3-(pyrrol-2-yl)propenoate, C₈H₉NO₂, (3), methyl (E)-3-(imidazol-2-yl)propenoate, C₇H₈N₂O₂, (4), and methyl (Z)-3-(imidazol-2-yl)propenoate, C₇H₈N₂O₂, (5), are reported. In the pyrrole and imidazole derivatives, (3) and (4), the N—H function has an s—Z configuration with respect to the propenoate chain, whereas in the urocanate, (2), protonation has occurred at the N atom further from the side chain. In (5) an intramolecular N—H...O hydrogen bond causes a relative widening of the angles in the side chain. In all four compounds, both the azole rings and the side chains are almost planar. In the hemihydrate of (2) there is extensive hydrogen bonding, primarily of the type N—H...O but supplemented by much longer C—H...O interactions. In (3) and (4) the hydrogen bonding is much simpler, with molecules linked into ribbons via N—H...O contacts.

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