What is "geminal diol"

n. (context organic chemistry English) Any diol in which the two hydroxy functional groups are attached to the same carbon atom.

A geminal diol (or gem-diol for short) is any organic compound having two hydroxyl functional groups (- O H) bound to the same carbon atom.

The simplest geminal diol is methanediol CHO or HC(OH). Other examples are dihydroxymalonic acid HOOC-C(OH)-COOH and decahydroxycyclopentane (C(OH)).

Geminal diols are a subclass of the diols, which in turn are a special class of alcohols.

The two hydroxyls in a geminal diol are easily converted to a carbonyl or keto group C=O by loss of one water molecule, thus turning the diol into a ketone. Conversely, ketones tend to combine with water to form the corresponding geminal diols. The equilibrium in water solution may be shifted towards either compound; for example, the equilibrium constant for the conversion of acetone (HC)C=O to propane-2,2-diol (HC)C(OH) is about 10,

Peter Taylor (2002), Mechanism and synthesis, Book 10 of Molecular world. Open University, Royal Society of Chemistry; ISBN 0-85404-695-X. 368 pages.

while that of formaldehyde HC=O to methanediol HC(OH) is 10, and that of hexafluoroacetone (FC)C=O to hexafluoropropane-2,2-diol (FC)C(OH) is about 10. In some cases, such as decahydroxycyclopentane and dodecahydroxycyclohexane, the geminal diol is stable while the ketone is not.