Planar versus non-planar: The important role of weak C—H...O hydrogen bonds in the crystal structure of 5-methylsalicylaldehyde

Abstract

The crystal structure of 5-methylsalicylaldehyde (5-MSA; systematic name 2-hydroxy-5-methylbenzaldehyde), C8H8O2, was discovered to be a textbook example of the drastic structural changes caused by just a few weak C—H...O interactions due to the additional methylation of the aromatic ring compared to salicylaldehyde SA. This weak intermolecular 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 molecule 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

• crystal structure
• 5-MSA
• organic
• salicylic acid
• hydrogen bonds