Question

How do you name this compound?

Answer 1

The name is (`E`)-3-carboxypenta-1,3-diene.

Explanation:

The "new" (2013) IUPAC rules give chain length priority over functional groups.

The longest chain contains five carbon atoms, so the base name is
penta-1,3-diene.

There is a `"COOH"` group on `"C3"`, so the name becomes
3-carboxypenta-1,3-diene.

Finally, the `"C3=C4"` double bond has the `E"` configuration because the highest-priority groups (carboxy and methyl) are on opposite sides of the bond.

The IUPAC name is (`E`)-3-carboxypenta-1,3-diene.