Besides vanillin, other fragrant aromatic compounds include anisaldehyde, cinnamaldehyde, and coumarin. How would you predict where bromination would take place in these structures?

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Answer 1 · 2016-06-24T23:49:52

Here's how I would argue.

Anisaldehyde

The structure of anisaldehyde is

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The aldehyde group directs substituents to the meta positions ( $C3 and C5$ $"C3 and C5"$ ).

The methoxy group also directs substituents to the ortho positions ( $C3 and C5$ $"C3 and C5"$ ).

∴ The bromination product is 3-bromo-4-methoxybenzaldehyde.

Cinnamaldehyde

The structure of cinnamaldehyde is

The $C=C$ $"C=C"$ double bond in the side-chain is more reactive than the benzene ring.

Hence, we will get addition across the external bond.

The bromination product is 2,3-dibromo-3-phenylpropanal.

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Coumarin

The structure of coumarin is

The alkene double bond is more reactive than those in the benzene ring.

∴ We will get addition of bromine across the double bond.

The product will be 3,4-dibromocoumarin.

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