Planar versus non-planar: The important role of weak C-H⋯O hydrogen bonds in the crystal structure of 5-methyl-salicyl-aldehyde

Ulrich Baisch; Marie Christine Scicluna; Christian Näther; Liana Vella-Zarb

doi:10.1107/S2056989017000238

Planar versus non-planar: The important role of weak C-H⋯O hydrogen bonds in the crystal structure of 5-methyl-salicyl-aldehyde

Acta Crystallogr E Crystallogr Commun. 2017 Jan 13;73(Pt 2):155-158. doi: 10.1107/S2056989017000238. eCollection 2017 Feb 1.

Authors

Ulrich Baisch¹, Marie Christine Scicluna¹, Christian Näther², Liana Vella-Zarb¹

Affiliations

¹ Department of Chemistry, University of Malta, Msida, MSD 2080, Malta.
² Anorganische Chemie, Christian-Albrechts-Universität zu Kiel, Max-Eyth-Str 2, 24118 Kiel, Germany.

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-aldehyde SA. This weak inter-molecular hydrogen bonding is observed between aromatic or methyl carbon donor atoms and hydroxyl or aldehyde acceptor oxygen atoms with d(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).

Keywords: 5-MSA; crystal structure; hydrogen bonds; organic; salicylic acid.