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Thursday 31 July 2008

Definition: In organic chemistry, a ketone is a type of compound which contains a carbonyl group (C=O) bonded to two other carbon atoms in the form: R1(CO)R2.

Neither of the substituents R1 and R2 may be equal to hydrogen (H). Where either R group is a hydrogen atom, the compound is known as an aldehyde.

A carbonyl carbon bonded to two carbon atoms distinguishes ketones from carboxylic acids, aldehydes, esters, amides, and other oxygen-containing compounds. The double-bond of the carbonyl group distinguishes ketones from alcohols and ethers.

The simplest ketone is acetone, CH3-CO-CH3 (systematically named propanone).

The carbon atom adjacent to a carbonyl group is called the α-carbon. Hydrogens attached to this carbon are called α-hydrogens.

In the presence of an acid catalyst the ketone is subjected to so-called keto-enol tautomerism. The reaction with a strong base gives the corresponding enolate. A diketone is a compound containing two ketone groups.

Acetone, acetoacetate and beta-hydroxybutyrate are ketones (or ketone bodies) generated from carbohydrates, fatty acids and amino acids in humans and most vertebrates.

Ketones are elevated in blood after fasting including a night of sleep, and in both blood and urine in starvation, hypoglycemia due to causes other than hyperinsulinism, various inborn errors of metabolism, and ketoacidosis (usually due to diabetes mellitus).

Although ketoacidosis is characteristic of decompensated or untreated type 1 diabetes, ketosis or even ketoacidosis can occur in type 2 diabetes in some circumstances as well.

Acetoacetate and beta-hydroxybutyrate are an important fuel for many tissues, especially during fasting and starvation.

The brain, in particular, relies heavily on ketone bodies as a substrate for lipid synthesis and for energy during times of reduced food intake.

At the NIH, Dr. Richard Veech refers to ketones as "magic" in their ability to increase metabolic efficiency, while decreasing production of free radicals, the damaging byproducts of normal metabolism.

His work has shown that ketone bodies may treat neurological diseases such as Alzheimer’s and Parkinson’s disease, and the heart and brain operate 25% more efficiently using ketones as a source of energy.

Research has also shown ketones play a role in reducing epileptic seizures with the so-called high-fat, near-zero carbohydrate Ketogenic Diet.

See also

- ketoacidosis