When ethanal CH3CHO undergoes a nucleophilic addition reaction with aqueous sodium hydroxide NaOH , a hydroxide ion OH- acts as a nucleophile and attacks the carbonyl carbon of ethanal. This results in the formation of an alkoxide intermediate, which then picks up a proton H+ from the surrounding water molecules to form the final product, which is a hydrate of ethanal, also known as a geminal diol.The product formed is ethane-1,1-diol CH3CH OH 2 .