Methyl 4-bromocrotonate is a small molecule with three useful features lined up along a short carbon chain: A bromine atom. A carbon-carbon double bond. And an ester. To an organic chemist, those aren't just structural details.
They're three different places where chemistry can happen. The bromine can be replaced, allowing the molecule to attach to another molecular fragment. The double bond can undergo addition, reduction, oxidation, or other transformations.
Global Chemical Database