Naming Aldehydes IUPAC:Replace -e with -al The aldehyde carbon is number 1. If -CHO is attached to a ring,use the suffix -carbaldehyde. CHO Example 2-cyclopentenecarbaldehyde cyclopent-2-en-1-carbaldehyde Naming Aldehydes IUPAC: Replace - e with -al. The aldehyde carbon is number 1. If -CHO is attached to a ring, use the suffix -carbaldehyde. Example CHO 2-cyclopentenecarbaldehyde cyclopent-2-en-1-carbaldehyde