Basic Organic Nomenclature

Aldehydes

Suffix:    -al

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 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 names 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 cycloakanecarbaldehyde (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 in bold) and should be memorized.

Examples naming simple aldehydes:

Compound Name
Line Drawing
3D Model
methanal
or
formaldehyde
ethanal
or
acetaldehyde
 propanal
butanal
cyclobutyl
carbaldehyde
or
cyclobutanecarbaldehyde
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-cyclohexenecarboxaldehyde
2-mercapto-4-oxoheptanal *

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

Aldehydes as Substituents:

In more complex molecules with higher priority functional groups, the aldehyde, same as a keto group, is named as an oxo- substituent. It is located by numbering the longest chain of carbons (according to the higher priority functional group) and locating the carbon atom of the carbonyl group by this numbering scheme. It is also named as a methanoyl- or formyl group when attached to a ring. Examples of these structures will be given in the subsequent pages.
 

Tutorial Quiz: Aldehydes

Next Page: Nitriles

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