Question

Draw all resonance structures for each compound and use the resonance structures to determine if the substituent has an electron-donating or electron-withdrawing resonance effect.

Short answer

a. The substituent acts electron-donating resonance effect.

b. The substituent acts electron-withdrawing resonance effect.

Step-by-step solution

Resonance

The resonance involves the formation of hypothetical structures which are obtained by the delocalization of electrons.

• The electron-donating group delocalizes the negative charge.

The electron-withdrawing group delocalizes the positive charge.

Explanation

a. The is an electron-withdrawing group because O is an electronegative atom, but it can act as an electron-donating group in the benzene ring due to the presence of lone pair on the O atom.

Therefore, the negative charge is delocalized in the benzene ring.

b. The is an electron-withdrawing group because the CO group tends to accept electrons. Therefore, the positive charge is delocalized in the benzene ring.