The IUPAC name of the compound \( CH_3 = CH - CH = CH - CHO \) is pent-2,4-enal.
The compound consists of a 5-carbon chain with two double bonds at positions 2 and 4.
The aldehyde group (\( -CHO \)) is located at the end of the chain, and the suffix "-al" is used to indicate the aldehyde functional group.
Thus, the IUPAC name is pent-2,4-enal.