| Addition Reaction | Elimination Reaction | |
|---|---|---|
Process | Two molecules combine in an addition reaction to form a single addition product (adduct).
| Elimination reaction involves loss of two groups and formation of a new bond. |
Mechanism | The addition can take place by heterolytic, homolytic, or pericyclic methods. | Elimination takes place either by heterocyclic mechanism or pericyclic. |
| Groups Involved and Product Formed | It occurs in molecules containing unsaturated functional groups like alkenes (C=C), alkynes (C≡C), aldehydes (RCHO), ketones (R2CO), imines (C=N), and between two free radicals. A leaving group has no role in addition reactions. | It occurs in molecules containing a leaving group like a halogen and the product formed by elimination is unsaturated (C=C or C≡C). |
Changes observed in Bonds | Here, in the addition reactions, the number of σ-bonds in the substrate molecule increases while one or more π-bonds are reduced. | In elimination reactions, there is a decrease in the number of σ-bonds in the substrate molecule which is compensated by the formation of new π-bonds. |
Reaction conditions | The free radical and pericyclic additions are nonpolar additions, requiring a nonpolar reaction medium. The addition reactions that prefer heterolytic pathways involve ionic intermediates, so polar solvents are preferred. | Elimination reaction requires a base. Higher temperature also favours elimination reaction.
|
| Subtypes | Heterolytic addition is of two types- Nucleophilic and electrophilic. Others are free radical and pericyclic. | E1, E2, and E1cb and three subtypes of the elimination reaction mechanism of which E2 is the most common. |
Organic chemistry is mainly about reactions, so naturally identifying the types of reactions is crucial since it enables one to anticipate the results of a reaction. The chapter on common reaction types (Introductory Organic Chemistry Course) covers various types such as addition, elimination, rearrangement, substitution, decomposition, and oxidation-reduction reactions. The information provided is sufficient to gain an initial understanding of these reaction types without getting overwhelmed by mechanistic details.
Related Reading- Common Reaction Types in Organic Chemistry
