Aldehydes

[lenadub]

Why aromatic aldehydes are less reactive than aliphatic aldehyds?

[burningbend]

probably just sterics

[chemisttree]

It depends on what you mean by reactive. If a particular reaction relies on an initially formed enol, it is obvious why the aliphatic aldehyde would be more reactive than the aromatic one, for example.

[Ygggdrasil]

First consider what features of aldehydes make them reactive.