Study of the Influence of the Change from Methyl to Isopropyl Substituents in 1-(2,4,6-trialkylphenyl)ethanol on the Point Group Symmetry of the 0-D Hydrogen-Bonded Moiety

Abstract

The steric hindrance in molecules of 1-(2,4,6-trimethylphenyl)ethanone and 1-(2,4,6-triisopropylphenyl)ethanone were shown to substantially differentiate the options of synthesis of the respective alcohols. The former was obtained with a yield of 12% with a mild reducing agent, i.e., NaBH4, as well as in vapor phase transfer hydrogenation (22% yield at 673 K) over MgO, whereas the latter was not formed at all under those conditions. The only agent that was able to reduce both ketones was LiAlH4. The single crystals of the two alcohols were obtained and their structures were determined. The symmetry of the 0-D hydrogen-bonded networks of molecules in these crystals was analyzed. It was shown that the methyl substituent allows the molecules to form hexameric rings, whereas the isopropyl-substituted molecules formed tetrameric ones. In both cases, there were two types of rings in the cell, but four types of molecules forming tetramers and only three types of molecules in the hexamers. These structures were compared to similar structures formed by other molecules found in the Cambridge Structural Database via hydrogen bonding. Moreover, the single crystal of 1-(2,4,6-triisopropylphenyl)ethanone was obtained to explain if either the hydrogen bonding or the presence of isopropyl groups influences the angles in the molecules.

Keywords

• ketone reduction
• steric hindrances
• hydrogen bonding
• hexamers
• tetramers