Question

explain why formaldehyde is more reactive than acetone

Answer 1

The carbon atom has a partial positive charge, and the oxygen atom has a partially negative charge. Aldehydes are usually more reactive toward nucleophilic substitutions thanketones because of both steric and electronic effects. ... Thus, steric hindrance is less in aldehydes than in ketones.
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Answer 2

Due to this the electron density on carbonyl carbon increases making it less electrophilic ,for the attack of a nucleophile while in case of formaldehyde there are no methyl groups so it is more reactive than acetone