which is more reactive to nucleophillic addition reactions, benzaldehyde or propanal?

Hi Jennifer,

Very good question!

 

Well, aromatic aldehydes in general are less reactive than aliphatic aldehydes. This is due to the reason that the electron-donating resonance effect (+R effect) of the benzene ring increases the electron density of the carbonyl carbon, thereby repelling the nucleophiles. This can be understood by the following resonating structures of benzaldehyde.

 

 

 

So, now it must have been clear that benzaldehyde is less stable than propanal towards nucleophilic addition reactions.

 

Hope, it is clear now.

Cheers!