Crystal structures and Hirshfeld surfaces of four meth-oxy-benzaldehyde oxime derivatives, 2-MeO- X C 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 )-meth-oxy-benzaldehyde oxime derivatives, namely (2-meth-oxy-benzaldehyde oxime, 1 , 2,3-di-meth-oxy-benzaldehyde oxime, 2 , 4-di-meth-oxy-benzaldehyde oxime, 3 , and 2,5-di-meth-oxy-benzaldehyde oxime, 4 , are discussed. The arrangements of the 2-meth-oxy group and the H atom of the oxime unit are s-cis in compounds 1 - 3 , but in both independent mol-ecules of compound 4 , the arrangements are s-trans . There is also a difference in the conformation of the two mol-ecules in 4 , involving the orientations of the 2- and 5-meth-oxy groups. The primary inter-molecular O-H(oxime)⋯O(hy-droxy) hydrogen bonds generate C (3) chains in 1 and 2 . In contrast, in compound 3 , the O-H(oxime)⋯O(hy-droxy) hydrogen bonds generate symmetric R 2 2 (6) dimers. A more complex dimer is generated in 4 from the O-H(oxime)⋯O(hy-droxy) and C-H(2-meth-oxy)⋯O(hy-droxy) hydrogen bonds. In all cases, further inter-actions, C-H⋯O and C-H⋯π or π-π, generate three-dimensional arrays. Hirshfeld surface and fingerprint analyses are discussed.