One further comparison: Aromatic aldehydes, such as benzaldehyde, are less reactive in nucleophilic addition reactions aliphatic aldehydes. The electron-donating resonance effect of the aromatic ring makes the carbonyl group less eletrophilic than the carbonyl group of an aliphatic aldehyde. Comparing eletrostatic potential maps of formaldehyde and benzaldehyde, for example, shows thats the carbonyl carbon atom is less positive (less blue) in the aromatic aldehyde.