Why Formaldehyde is more reactive then other aldehydes? justify .

The reactivity of Aldehydes depend upon two factors .

1 Steric effect :- The reactivity of aldehyde depends upon the fact that the nucleophile will attack on the Carbon atom of the carbonyl group. If it is less crowded the nucleophile can easily approach it and can easily react. So lesser is the hinderance more will be the reactivity. In case of formaldehyde the carbonyl atom is joined to two Hydrogen atoms and the carbon atom of carbonyl group is easily approachable . It is shown below :-

2 Inductive effect :- The +I effect increase the electron density on carbon atom of carbonyl group, which makes it less polar and less electrophillic in nature. But in case of formaldehyde there is not any electron releasing or electron donating group present. Thus the carbon atom of carbonyl group is more electrophillic in nature so it is more reactive .