Reduction

In organic chemistry, reduction is the addition of hydrogen or the removal of oxygen. In equations the reducing agent is shown as [H].Aldehydes are reduced to primary alcohols and ketones to secondary alcohols using NaBH₄, for example CH₃CHO + 2[H] → CH₃CH₂OH.The hydride ion H^- from NaBH₄ acts as a nucleophile and attacks the δ+ carbon of the C=O group. This is nucleophilic addition.Reduction is the reverse of the oxidation of alcohols. Alkenes are reduced to alkanes by hydrogen with a nickel catalyst, and nitrobenzene is reduced to phenylamine by tin and concentrated HCl.