Aldehyde group

Aldehyde Group

An aldehyde group is a functional group consisting of a carbonyl center (a carbon double-bonded to oxygen) with the carbon atom also bonded to hydrogen and to an R group, which is any generic alkyl or side chain. The group—without R—is the aldehyde functional group, also known as formyl group. Aldehydes are common in organic chemistry. Aldehydes feature an sp2-hybridized, planar carbon center that is connected by a double bond to oxygen and a single bond to hydrogen. The C-H bond is not ordinarily acidic. Because they do not have leaving groups, aldehydes tend to be less reactive than ketones. Aromatic aldehydes are less reactive and more stable than aliphatic aldehydes, as the aromatic ring can delocalize the charge of the carbonyl.

Structure and Bonding

The carbonyl group (C=O) is polar because oxygen is more electronegative than carbon, and thus, it draws more than its fair share of electrons. The carbonyl carbon and oxygen share a double bond. The remaining two bonds are to other carbon atoms or hydrocarbon atoms. The most important aldehyde is formaldehyde, which is a gas at room temperature.

Nomenclature

In IUPAC nomenclature, aldehydes have priority over many other functional groups. The aldehyde functional group is named by replacing the '-e' ending of the parent alkane with '-al', so that H2C=O would be named "methanal". In traditional nomenclature, the -CHO, characteristic of aldehydes, is attached to the name of the corresponding acid by replacing the -ic acid ending with -aldehyde.

Reactions

Aldehydes are highly reactive and participate in many reactions. In addition to polymerization, aldehydes undergo a variety of condensation reactions. Aldehydes are commonly used in aldol reactions, producing a compound with both a hydroxyl and an aldehyde group.

Biological Importance

Aldehydes play an important role in many biochemical processes. For example, in the Calvin cycle, which occurs in the chloroplasts of plant cells, the compound 3-phosphoglyceraldehyde is a key intermediate in the conversion of carbon dioxide to glucose.

See Also

• Ketone
• Carboxylic acid
• Organic chemistry
• Biochemistry