Crystal structures and Hirshfeld surfaces of four methoxybenzaldehyde oxime derivatives, 2-MeO-XC6H3C=NOH (X = H and 2-, 3- and 4-MeO): different conformations and hydrogen-bonding patterns

Abstract

The crystal structures of four (E)-methoxybenzaldehyde oxime derivatives, namely (2-methoxybenzaldehyde oxime, 1, 2,3-dimethoxybenzaldehyde oxime, 2, 4-dimethoxybenzaldehyde oxime, 3, and 2,5-dimethoxybenzaldehyde oxime, 4, are discussed. The arrangements of the 2-methoxy group and the H atom of the oxime unit are s-cis in compounds 1–3, but in both independent molecules of compound 4, the arrangements are s-trans. There is also a difference in the conformation of the two molecules in 4, involving the orientations of the 2- and 5-methoxy groups. The primary intermolecular O—H(oxime)...O(hydroxy) hydrogen bonds generate C(3) chains in 1 and 2. In contrast, in compound 3, the O—H(oxime)...O(hydroxy) hydrogen bonds generate symmetric R 2 2(6) dimers. A more complex dimer is generated in 4 from the O—H(oxime)...O(hydroxy) and C—H(2-methoxy)...O(hydroxy) hydrogen bonds. In all cases, further interactions, C—H...O and C—H...π or π–π, generate three-dimensional arrays. Hirshfeld surface and fingerprint analyses are discussed.