Elimination reaction is best described as

• A. Removal of a molecule from a saturated molecule to form an unsaturated molecule
• B. Addition of a molecule to a saturated molecule
• C. Substitution of a leaving group by a nucleophile
• D. Isomerization to a different arrangement

Answer: (D)

Elimination reactions are about forming a double bond by removing atoms from a saturated molecule. Typically, a leaving group on one carbon and a hydrogen on an adjacent carbon are removed in one step (or in two steps, via a carbocation), and this loss of atoms leads to the formation of a C=C bond, producing an unsaturated product.

This is different from addition, which adds atoms across a double bond; substitution, which replaces a leaving group with another nucleophile without creating a double bond; and isomerization, which rearranges atoms without changing the degree of saturation. Elimination often proceeds via an E2 mechanism with a strong base (concerted) or an E1 mechanism with a good leaving group and a carbocation intermediate (depending on substrate and conditions).