Aldehydes

1. The suffix -al is appended to the name of the hydrocarbon corresponding to the longest carbon chain that includes the aldehyde carbon. Remember that alkane + -al becomes alkanal with the e omitted, and because the al function is necessarily at C1, the -1- is redundant and is omitted:

Dialdehydes are named as -dials. Thus OHCCH2CH2CH2CH2CHO is hexanedial.

2. The simplest aldehyde is methanal, HCHO, which is familiarly known as formaldehyde. However, when aldehydes are named as derivatives of methanal, they usually are called carbaldehydes, and the suffix "carbaldehyde" refers to the −CHO group. This system is used where the hydrocarbon group is not a chain, but a ring, and the CHO group can be thought of as a one-carbon chain:

3. When the −CHO group is a substituent on the parent chain or ring and it ranks below another functional group, it properly is designated by the prefix methanoyl. However, the prefix formyl also is used:

4. Trivial names are used for many simple aldehydes, some of which are shown below in parentheses: