Addition reaction

"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."

"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."

"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 NaBH4 or LiAlH4 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."

"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."

"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."

"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."