Definition
Aldehydes are organic compounds with the general structure R-CHO, where R can be aliphatic and aromatic. The functional group consists of a carbonyl group (C=O) with a hydrogen atom attached to its carbon atom. In formaldehyde, R is a hydrogen atom (HCHO). Aldehydes can be obtained, for example, by oxidation of alcohols or by reduction of carboxylic acids.
Nomenclature
The suffix -aldehyde is used to form the trivial names. Official nomenclature uses the suffix -al, so for example hexane + -al = hexanal.
Representative
A small selection of aldehydes:
- Acetaldehyde
- Anisaldehyde
- Benzaldehyde
- Formaldehyde
- Furfural
- Retinal (vitamin A)
- Cinnamaldehyde
- Vanillin
Properties
- Aldehydes are polar molecules. This due to the higher electronegativity of oxygen. The carbon is partially positively charged, the oxygen partially negatively charged.
- They are hydrogen bond acceptors, but not hydrogen bond acceptors. Therefore, their boiling point is lower than that of comparable alcohols.
- Some aldehydes have an aromatic odor or taste.
- Aldehydes are reactive and susceptible to oxidation.
Reactions
Numerous chemical reactions are possible with aldehydes. Two important examples are listed below.
- Aldehydes can be reduced to alcohols and oxidized to carboxylic acids (see above).
- Aldehydes can be substituted with a nucleophile. The reason lies in the partial positive charge of the carbon of the carbonyl group.
In pharmacy
- As a functional group in active ingredients and excipients.
- For chemical syntheses.
- As a disinfectant.
