# Addition reaction

An addition reaction is in its simplest terms an organic reaction where two or more molecules combine to form a larger one.

## Quotes

* Just as the chemistry of alkenes is dominated by addition reactions, the preparation of alkenes is dominated by elimination reactions. Additions and eliminations are, in many respects, two sides of the same coin.
** John McMurry, Organic Chemistry 8th ed. (2012), Ch. 8 : Alkenes: Reactions and Synthesis.
* As a general rule, electrophiles undergo addition reactions with alkynes much as they do with alkenes. Take the reaction of alkynes with HX, for instance. The reaction often can be stopped after addition of 1 equivalent of HX, but reaction with an excess of HX leads to a dihalide product. For example, reaction of 1-hexyne with 2 equivalents of HBr yields 2,2-dibromohexane.
** John McMurry, Organic Chemistry 8th ed. (2012), Ch. 9 : Alkynes: An Introduction to Organic Synthesis.
* The nucleophilic addition reactionis the most common general reaction type for aldehydes and ketones. Many different kinds of products can be prepared by nucleophilic additions. Aldehydes and ketones are reduced by NaBH$_4$ or LiAlH$_4$ to yield primary and secondary alcohols, respectively. Addition of Grignard reagents to aldehydes and ketones also gives alcohols (secondary and tertiary, respectively), and addition of HCN yields cyanohydrins. Primary amines add to carbonyl compounds yielding imines, or Schiff bases, and secondary amines yield enamines. Reaction of an aldehyde or ketone with hydrazine and base gives an alkane (the Wolff–Kishner reaction). Alcohols add to carbonyl groups to yield acetals, which are valuable as protecting groups. Phosphorus ylides add to aldehydes and ketones in the Wittig reaction to give alkenes. α, β-Unsaturated aldehydes and ketones often react with nucleophiles to give the product of conjugate addition, or 1,4 addition. Particularly useful are the conjugate addition of an amine and the conjugate addition of an organic group by reaction with a diorganocopper reagent.
** John McMurry, Organic Chemistry 8th ed. (2012), Ch. 19. Aldehydes and Ketones: Nucleophilic Addition Reactions.
* An addition reaction is a reaction in which a molecule adds to a molecule containing a double bond, converting the double bond into a single bond. Because of this property of readily combining with other substances such as the halogens, ethylene and related hydrocarbons are said to be unsaturated. Ethylene is the first member of a homologous series of hydrocarbons, called the ethylene series.
** Linus Pauling, College Chemistry Chap. 7. Carbon and Compounds of Carbon.
* We turn our attention to alkenesand alkynes, compounds that contain one and two π bonds, respectively. Because π bonds are easily broken, alkenes and alkynes undergo addition, the third general type of organic reaction. These multiple bonds also make carbon atoms electron rich, so alkenes and alkynes react with a wide variety of electrophilic reagents in addition reactions.
** Janice G. Smith, Organic Chemistry, 3rd Edition (2011), Ch. 10 : Alkenes.
* Many alkenes possess defined stereochemistry (E and Z) and, as we shall see in our discussions, many of their addition reactions proceed in a stereochemically defined manner.
** K. Peter C. Vollhardt, Neil E. Schore (2011) Organic chemistry : structure and function 6th ed. Chap. 12. Reactions of Alkenes.