Basic Organic Nomenclature

Aldehydes

Substitutive suffix:    -al

Substitutive prefix:    -oxo-

Aldehydes are the second compound containing the carbonyl group ( C=O ) that we will exam. In aldehydes one of the two groups attached to the carbonyl carbon atom is an alkyl group, the other is a hydrogen atom. This means that aldehyde carbonyl group must occur at the end of a chain of atoms (i.e. R-CHO).

When an aldehyde group is the highest priority functional group present in the molecule, it is named as an alkanal (note, the -e is dropped). The numbering scheme used will be the one that gives the carbonyl carbon atom the lowest possible number (i.e. number 1). Other functional groups are located by this numbering scheme. Since the carbonyl group is always at carbon number 1, there is no need to indicate the location.

It is possible to have the -CHO group directly attached to a ring, and if it is the highest priority group in the molecule, the ring is a substituent to the aldehyde and it is named as a cycloalkyl carbaldehyde or cycloalkanecarbaldehyde (an older way is as a carboxaldehyde). There are a number of compounds which were named before IUPAC developed the standardized nomenclature rules. Many of these compounds are still referred to by these common names. The common names for the more common compounds will be included (underlined) and should be memorized.

Examples naming simple aldehydes:

Compound Name	Line Drawing	3D Model
methanal or formaldehyde
ethanal or acetaldehyde
propanal
butanal
cyclobutanecarbaldehyde or cyclobutyl carbaldehyde
pentanedial *

* note: the -e as added with the di- prefix of the dial, numbers for the two aldehydes are not necessary.

Examples naming more complex aldehydes:

Compound Name	Line Drawing
4,4-dimethylpentanal
4-pentenal
4-amino-3-isopropylhexanal
4-chloro-2-cyclohexenecarbaldehyde or 4-chloro-2-cyclohexenyl carbaldehyde
4-oxo-2-sulfanylheptanal *

* note: a keto group is lower in priority than an aldehyde so it appears as an -oxo- substituent.

Aldehydes as Substituents:

Name	Formula	Line Drawing
formyl (preferred to methanoyl)	HCO-
-oxo-	=O

For example, a CHOCH₂CH₂CH₂-R group is a 3-formylpropyl group or a 4-oxobutyl group.