Knowledge Bank

The infra-red spectra of a series of molecules containing carbonyl and hydroxyl groups (e.g. $CH3COCH2OH$) were measured in the vapor phase between $4000cm-1$ and $300cm-1$ The main results are that only one band is observed for each of the OH and $C=O$ stretching modes, their frequencies being close to those of carboxylic acid monomers ($3570cm-1$, and $1760cm-1$), while the OH torsional mode is found at a much lower frequency ($375cm-1$) Pyruvic acid ($CH2COCOOH$) appears to be somewhat unusual in that the $V8(OH)$ band of one of the two monomeric conformations is observed at $3460cm-1$. These results are interpreted in terms of planar intra-molecular hydrogen bonds and compared with other types of intra-molecular hydrogen bonds such as in the 2-substituted ethanols.