Geminal diol
Encyclopedia
A geminal diol is any organic compound
having two hydroxyl
functional groups (-O
H
) 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.
Geminal diols are a subclass of the diol
s, which in turn are a special class of alcohol
s.
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
(H3C)2C=O to propane-2,2-diol (H3C)2C(OH)2 is about 10−3, while that of formaldehyde
H2C=O to methanediol H2C(OH)2 is 10+3, and that of hexafluoroacetone
(F3C)2C=O to hexafluoropropane-2,2-diol (F3C)2C(OH)2 is about 10+6. In some cases, such as decahydroxycyclopentane and dodecahydroxycyclohexane
, the geminal diol is stable while the ketone is not.
Organic compound
An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon. For historical reasons discussed below, a few types of carbon-containing compounds such as carbides, carbonates, simple oxides of carbon, and cyanides, as well as the...
having two hydroxyl
Hydroxyl
A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...
functional groups (-O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
H
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
) bound
Covalent bond
A covalent bond is a form of chemical bonding that is characterized by the sharing of pairs of electrons between atoms. The stable balance of attractive and repulsive forces between atoms when they share electrons is known as covalent bonding....
to the same carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
atom.
The simplest geminal diol is methanediol
Methanediol
Methanediol, also known as formaldehyde monohydrate or methylene glycol, is a chemical compound with chemical formula CH4O2, or H2C2...
CH4O2 or H2C(OH)2. Other examples are dihydroxymalonic acid
Dihydroxymalonic acid
Dihydroxymalonic acid is an organic compound with formula C3H4O6 or HO--C2--OH, found in some plants such as alfalfa and in beet molasses.The compound may also be called dihydroxymesoxalic acid, dihydroxypropanedioic acid...
HOOC-C(OH)2-COOH and decahydroxycyclopentane
Decahydroxycyclopentane
Decahydroxycyclopentane is an organic compound with formula C5O10H10 or C510. It is a fivefold geminal diol on a cyclopentane backbone.The compound can be regarded as the fivefold hydrate of cyclopentanepentone. Indeed, the product referred to in the literature and trade as "cyclopentanepentone...
(C(OH)2)5.
Geminal diols are a subclass of the diol
Diol
A diol or glycol is a chemical compound containing two hydroxyl groups A geminal diol has two hydroxyl groups bonded to the same atom...
s, which in turn are a special class of alcohol
Alcohol
In chemistry, an alcohol is an organic compound in which the hydroxy functional group is bound to a carbon atom. In particular, this carbon center should be saturated, having single bonds to three other atoms....
s.
The two hydroxyls in a geminal diol are easily converted to a carbonyl
Carbonyl
In organic chemistry, a carbonyl group is a functional group composed of a carbon atom double-bonded to an oxygen atom: C=O. It is common to several classes of organic compounds, as part of many larger functional groups....
or keto group C=O by loss of one water molecule, thus turning the diol into a ketone
Ketone
In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...
. 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
Acetone
Acetone is the organic compound with the formula 2CO, a colorless, mobile, flammable liquid, the simplest example of the ketones.Acetone is miscible with water and serves as an important solvent in its own right, typically as the solvent of choice for cleaning purposes in the laboratory...
(H3C)2C=O to propane-2,2-diol (H3C)2C(OH)2 is about 10−3, while that of formaldehyde
Formaldehyde
Formaldehyde is an organic compound with the formula CH2O. It is the simplest aldehyde, hence its systematic name methanal.Formaldehyde is a colorless gas with a characteristic pungent odor. It is an important precursor to many other chemical compounds, especially for polymers...
H2C=O to methanediol H2C(OH)2 is 10+3, and that of hexafluoroacetone
Hexafluoroacetone
Hexafluoroacetone is a chemical compound with the formula CF3-CO-CF3. It is structurally similar to acetone, however its reactivity is markedly different. It comes in the form of a colourless, hygroscopic, nonflammable, highly reactive gas characterized by a musty odour...
(F3C)2C=O to hexafluoropropane-2,2-diol (F3C)2C(OH)2 is about 10+6. In some cases, such as decahydroxycyclopentane and dodecahydroxycyclohexane
Dodecahydroxycyclohexane
Dodecahydroxycyclohexane is an organic compound with molecular formula C6O12H12 or C612. It is a sixfold geminal diol with a cyclohexane backbone and can be regarded as a sixfold hydrate of cyclohexanehexone .-Dihydrate:...
, the geminal diol is stable while the ketone is not.