Geminal diol
A geminal diol (or gem-diol for short) is any organic compound having two hydroxyl functional groups (Template:Chem2) bound to the same carbon atom. Geminal diols are a subclass of the diols, which in turn are a special class of alcohols. Most of the geminal diols are considered unstable.
The simplest geminal diol is methanediol Template:Chem2 or Template:Chem2. Other examples are:
- dihydroxymalinic acid Template:Chem2
- decahydroxycyclopentane Template:Chem2
- chloral hydrate Template:Chem2
Reactions
Hydration equilibrium
Geminal diols can be viewed as ketone (or aldehyde) hydrates. The two hydroxyl groups in a geminal diol are easily converted to a carbonyl or keto group C=O by loss of one water molecule. Conversely, a keto group can combine with water to form the geminal hydroxyl groups.
The equilibrium in water solution may be shifted towards either compound. For example, the equilibrium constant for the conversion of acetone Template:Chem2 to propane-2,2-diol Template:Chem2 is about 10−3,[1] while that of formaldehyde Template:Chem2 to methanediol Template:Chem2 is 103.[2]
For conversion of hexafluoroacetone Template:Chem2 to the diol Template:Chem2, the constant is about 10+6, due to the electron withdrawing effect of the trifluoromethyl groups. Similarly, the conversion of chloral Template:Chem2 to chloral hydrate is strongly favored by influence of the trichloromethyl group.
In some cases, such as decahydroxycyclopentane and dodecahydroxycyclohexane, the geminal diol is stable while the corresponding ketone is not.
Geminal diols can also be viewed as extreme cases of hemiacetals, formed by reaction of carbonyl compounds with water, instead of with an alcohol.
See also
References
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- ↑ Peter Taylor (2002), Mechanism and synthesis, Book 10 of Molecular world. Open University, Royal Society of Chemistry; Template:ISBN. 368 pages.
- ↑ Eric V. Anslyn, Dennis A. Dougherty (2006), Modern physical organic chemistry. University Science Books. Template:ISBN. 1095 pages
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