The temperature-pressure phase diagram was determined for a crystal of squaric acid which consists of molecular sheets of [C4041 2skeletons and intervening protons. Under hydrostatic pressures, the paraelectric phase composed of the polar (Ci/,-distorted) molecules is realized even near 0 K due to a joint quantum motion of the protons and deforming molecular skeletons. Further application of pressure causes a disappearance of the 7r-bond alternation of the constituent molecule at all temperatures caused by enhanced motion of the protons.

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The infrared hydroxyl and carbonyl stretching absorption spectra of salicylic, mandelic, and α-hydroxyisobutyric acids have been measured in dilute carbon tetrachloride solutions. The spectral data indicate that the first two acids exist exclusively in an internally-bonded conformation, one where the phenolic and the alcoholic hydroxyl groups form a hydrogen bond with the carbonyl oxygen atom of the cis-carboxyl structure, while the last acid takes, apart from such a conformation, another internally-bonded conformation, one where the hydroxyl group of the trans-carboxyl structure interacts with the alcoholic oxygen atom.