title: Planarversusnon-planar: The important role of weak C-H⋯O hydrogen bonds in the crystal structure of 5-methyl-salicyl-aldehyde.
abstract: The crystal structure of 5-methyl-salicyl-aldehyde (5-MSA; systematic name 2-hy-droxy-5-methyl-benzaldehyde), C8H8O2, was discovered to be a textbook example of the drastic structural changes caused by just a few weak C-H⋯O inter-actions due to the additional methyl-ation of the aromatic ring compared to salicyl-aldehydeSA. This weak inter-molecular hydrogen bonding is observed between aromatic or methyl carbon donor atoms and hydroxyl or aldehyde acceptor oxygen atoms withd(D⋯A) = 3.4801 (18) and 3.499 (11) Å. The mol-ecule shows a distorted geometry of the aromatic ring with elongated bonds in the vicinity of substituted aldehyde and hydroxyl carbon atoms. The methyl hydrogen atoms are disordered over two sets of sites with occupancies of 0.69 (2) and 0.31 (2).
authors.affiliation: Department of Chemistry, University of Malta, Msida, MSD 2080, Malta.
authors.forename: Ulrich
authors.initials: U
authors.lastname: Baisch
authors.affiliation: Department of Chemistry, University of Malta, Msida, MSD 2080, Malta.
authors.forename: Marie Christine
authors.initials: MC
authors.lastname: Scicluna
authors.affiliation: Anorganische Chemie, Christian-Albrechts-Universität zu Kiel, Max-Eyth-Str 2, 24118 Kiel, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Näther
authors.affiliation: Department of Chemistry, University of Malta, Msida, MSD 2080, Malta.
authors.forename: Liana
authors.initials: L
authors.lastname: Vella-Zarb
keywords: 5-MSA; crystal structure; hydrogen bonds; organic; salicylic acid