Crystal structures and Hirshfeld surfaces of four meth­oxy­benzaldehyde oxime derivatives, 2-MeO-XC(6)H(3)C=NOH (X = H and 2-, 3- and 4-MeO): different conformations and hydrogen-bonding patterns

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.