Nucleophilic addition

Nucleophilic addition (see: nucleophilicity ) is a reaction mechanism in organic chemistry, in which a nucleophile ( anion or Lewis base ) engages a multiple bond. The nucleophile is the attacked compound added (addition). There is no exchange of atoms or groups of atoms instead (compare with: substitution).

  • 2.1 Nucleophilic addition to C -C multiple bonds,
  • 2.2 Nucleophilic addition to C -X -C multiple bonds
  • 3.1 Nucleophilic addition to C -C multiple bonds,
  • 3.2 Nucleophilic addition to C -X -C multiple bonds 3.2.1 oxygen as a nucleophile
  • 3.2.2 nitrogen nucleophile
  • 3.2.3 sulfur nucleophile
  • 3.2.4 carbanionic carbon as nucleophile

Reactants

Nucleophile

As nucleophiles various compounds can be used. These are electron-rich, mostly lone-pair -containing molecules or anions (see below: examples).

Multiple bonds

Nucleophilic additions may take place on different types of multiple bonds:

Course of the reaction

The addition of the nucleophile is usually controlled thermodynamically; the nucleophile is attached to the multiple bond that a stable anion possible results (compare the reasoning of the Markovnikov rule). The stabilization is carried out at CX multiple bonds by heteroatoms itself substituted at C-C multiple bonds by inductive effects of substituents, but in particular by substituents with - M effect. Since such substituents positivize the distant carbon atom of the double bond at the same time, the addition to this is favored kinetically.

Nucleophilic addition to C -C - multiple bonds,

The first step in this reaction is in the attack of the nucleophile to form a carbanion:

In the second step, the carbanion is reacted with an electron acceptor, usually a proton:

The formation of the carbanion is strongly favored by the substituents can stabilize it by resonance. One then speaks of a Michael addition, where the nucleophile is the anion of a CH -acidic compound.

Nucleophilic addition to C -X -C multiple bonds

CX multiple bonds come in the following atom groups:

  • Carbonyl
  • Thiocarbonyl
  • Isocyanate
  • Azomethine
  • Cyano group
  • Isocyano

Here a nucleophile to attack the carbon of a CX multiple bond. The other possibility is, that the first electron-withdrawing heteroatom is protonated in a preceding equilibrium, and then the carbon binds to the nucleophile.

Examples

Nucleophilic addition to C -C - multiple bonds,

  • Addition of ammonia or amines,
  • Addition of hydrogen cyanide
  • Michael addition of

Nucleophilic addition to C -X -C multiple bonds

The individual nucleophilic additions to CX multiple bonds can be divided into groups on the basis of the attacking nucleophile:

Oxygen as a nucleophile

Nitrogen as a nucleophile

  • Addition of primary amines: This reaction leads to a corresponding one of the hemiacetal compound ( hemiaminal ) which merges in a subsequent reaction with elimination of water in an azomethine.
  • Addition of secondary amine: This reaction leads ultimately to an enamine.
  • Addition of hydrazine
  • Addition of hydroxylamine
  • Mannich reaction

Sulfur nucleophile

  • Mercaptal formation
  • Bisulfite

Carbanionic carbon as nucleophile

  • Aldol reaction
  • Benzoin addition
  • Cyanohydrin synthesis
  • Knoevenagel condensation
  • Perkin reaction
  • Reformatsky reaction
  • Stobbe condensation
  • Strecker synthesis of amino acids
  • Wittig reaction

Cycloaddition | Electrophilic Addition | Electrophilic Substitution | Electrophilic Aromatic Substitution | elimination | Nucleophilic Addition | Nucleophilic aromatic substitution | Nucleophilic substitution | oxidation | Radical Addition | Radical Substitution | Reduction | rearrangement

Addition reaction Electron pair Triple bond Chemical reaction Michael reaction Chemical equilibrium Hydration reaction Benzoin condensation Strecker amino-acid synthesis Integrated Authority File
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