Geminal diol
![Geminal diols can be thought of as ketone (or aldehyde) hydrates](/Images/godic/202501/22/Ketone-hydrate-2D-skeletal2951.png")
A geminal diol (or gem-diol for short) is any organic compound having two hydroxyl functional groups (-OH) bound to the same carbon atom.
The simplest geminal diol is methanediol CH4O2 or H2C(OH)2. Other examples are dihydroxymalonic acid HOOC-C(OH)2-COOH and decahydroxycyclopentane (C(OH)2)5.