Which of the following reaction will not produce ketones?

Stephen's reaction

The correct answer is option 4. Stephen's reaction

Hydration of alkynes: This reaction can indeed produce ketones, especially for internal alkynes. The addition of water across the triple bond can lead to a carbonyl group \((C=O)\) formation.

Ozonolysis of substituted alkenes: This reaction breaks down alkenes using ozone \((O_3)\) followed by reduction. Depending on the substitution pattern of the alkene, it can lead to the formation of ketones as products.

Treating nitrile with a Grignard reagent: When a Grignard reagent (organometallic compound with a magnesium-halogen bond) reacts with a nitrile, it can form an ketone.

Stephen's reaction: This reaction involves the reduction of nitriles \((RCN)\) to aldehydes or imines using stannous chloride \((SnCl_2)\) and hydrochloric acid \((HCl)\). The resulting imines can further hydrolyze to aldehydes. However, ketones are not typically formed in Stephen's reaction.