The reactions to increase carbon chain length in A-Level Chemistry include: Aldol Condensation: An aldol condensation reaction involves the formation of a new carbon-carbon bond between two aldehyde or ketone molecules to form a more complex molecule with a longer carbon chain. Michael Addition: A Michael addition reaction involves the addition of a nucleophile to the carbonyl group of an aldehyde or ketone, leading to an increase in the length of the carbon chain.