STEREOPOPULATION CONTROL IN 3-(2,4-DIMETHYL-6-METHOXYPHENYL)-3-METHYLBUTYRIC ACID AND PROTON STABILITY IN HYDROGEN-BONDED CARBOXYLIC GROUPS

The crystal structure of 3-(2,4-dimethyl-6-methoxyphenyl)-3-methylbuty ric acid has been determined by X-rays: the asymmetric part of the uni t cell contains four molecules, rotational conformers, hydrogen-bonded into dimers. The apparent conformational preferences of the molecular side chain cannot be directly attributed to the trimethyl lock, but i s due to electrostatic interactions between substituents at the phenyl ring. Skew arrangements of hydrogen-bonded carboxylic groups are show n to stabilize the sites of the acidic protons in the crystalline stat e.