Chemistry · Aldehydes and Ketones

In the presence of concentrated H₂SO₄, acetaldehyde primarily undergoes polymerization to form paraldehyde. Concentrated sulfuric acid acts as a catalyst for the polymerization process, leading to the formation of a cyclic trimer. Other reactions such as dehydration and oxidation are not the main pathways under these conditions. Aldol condensation is incorrect here because it typically requires basic conditions rather than the acidic environment provided by concentrated sulfuric acid.

Dehydration: Incorrect. While dehydration involves the removal of water molecules, acetaldehyde does not primarily undergo a dehydration reaction in the presence of concentrated sulfuric acid.

Polymerization: Correct. In the presence of concentrated H₂SO₄, acetaldehyde can undergo polymerization to form paraldehyde, a trimer of acetaldehyde.

Aldol Condensation: Incorrect. Aldol condensation occurs under basic conditions, not with concentrated sulfuric acid, which is acidic.

Oxidation reaction: Incorrect. While acetaldehyde can be oxidized, this is not the primary reaction facilitated by concentrated sulfuric acid in this context.