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]s to form a ] (red) with expulsion of water (blue)]] ]s to form a ] (red) with expulsion of water (blue)]]
A '''condensation reaction''', is a ] in which two ]s or moieties (]) combine to form a larger molecule, together with the loss of a small molecule.<ref name="Gold">{{GoldBookRef|title=Condensation Reaction|file=C01238|year=1994}}</ref> Possible small molecules lost are ], ], ], or ] but most commonly in a biological reaction it is ]. A '''condensation reaction''', is a ] in which two ]s or ], often ]s, combine to form a larger molecule, together with the loss of a small molecule.<ref name="Gold">{{GoldBookRef|title=Condensation Reaction|file=C01238|year=1994}}</ref> Possible small molecules that are lost include ], ], ], or ], but most commonly in a biological reaction it is water.


When two separate molecules react, the condensation is termed ]. A simple example is the condensation of two ]s to form the ] characteristic of ]. This reaction example is the opposite of ], which splits a chemical entity into two parts through the action of the polar water molecule, which itself splits into ] and ] ions. Hence energy is required. When two separate molecules react, the condensation is termed ]. A simple example is the condensation of two ]s to form the ] characteristic of ]s. This reaction example is the opposite of ], which splits a chemical entity into two parts through the action of the polar ], which itself splits into ] and ] ions. Hence ] is required to form ]s via condensation.


If the union is between atoms or groups of the same molecule, the reaction is termed ] condensation, and in many cases leads to ring formation. An example is the ], in which the two ] groups of a single diester molecule react with each other to lose a small ] molecule and form a β-ketoester product. If the union is between ]s or groups of the same molecule, the reaction is termed ] condensation, and in many cases leads to ]. An example is the ], in which the two ] groups of a single diester molecule react with each other to lose a small ] molecule and form a β-ketoester product.


] ]


==Mechanism== ==Mechanism==
Many condensation reactions follow a ] or an ] ]. Other condensations, such as the ] are triggered by ] or ] conditions. Many condensation reactions follow a ] or an ] ]. Other condensations, such as the ] are triggered by ] or ] conditions.


==Condensation reactions in polymer chemistry== ==Condensation reactions in polymer chemistry==
In one type of polymerization reaction, a series of condensation steps take place whereby ]s or monomer chains add to each other to form longer chains. This is termed 'condensation polymerization' or ']', and occurs for example in the synthesis of ]s or ]s. It may be either a homopolymerization of a single monomer A-B with two different end groups that condense or a ]ization of two co-monomers A-A and B-B. Small molecules are usually liberated in these condensation steps, in contrast to ] reactions with no liberation of small molecules. In one type of ] reaction, a series of condensation steps take place whereby ]s or monomer chains add to each other to form longer chains called ]s. This is termed 'condensation polymerization' or ']', and occurs for example in the synthesis of ]s or ]s. It may be either a homopolymerization of a single monomer A-B with two different end groups that condense or a ]ization of two co-monomers A-A and B-B. Small molecules are usually liberated in these condensation steps, in contrast to ] reactions with no liberation of small molecules.


In general, condensation polymers form more slowly than addition polymers, often requiring heat. They are generally lower in molecular weight. Monomers are consumed early in the reaction; the terminal functional groups remain active throughout and short chains combine to form longer chains. A high conversion rate is required to achieve high molecular weights as per ]. In general, condensation polymers form more slowly than ]s, often requiring ]. They are generally lower in molecular weight. Monomers are consumed early in the reaction; the terminal ]s remain active throughout and short chains combine to form longer chains. A high conversion rate is required to achieve high molecular weights as per ].


Bifunctional monomers lead to linear chains (and therefore ] polymers), but, when the monomer ] exceeds two, the product is a ] chain that may yield a ] polymer. ] monomers lead to linear chains, and therefore ] polymers, but, when the monomer ] exceeds two, the product is a ] chain that may yield a ] polymer.


==Applications== ==Applications==
This type of reaction is used as a basis for the making of many important ]s, for example: ], ], and other ]s and various ]. It is also the basis for the laboratory formation of ]s and ]s. The reactions that form acid ]s from their constituent acids are typically condensation reactions. This type of reaction is used as a basis for the making of many important ]s, for example: ], ], and other ]s and various ]. It is also the basis for the laboratory formation of ]s and ]s. The reactions that form ] from their constituent acids are typically condensation reactions.


Many biological transformations are condensation reactions. ], ] synthesis, ] syntheses, ], and ]s are a few examples of this reaction. Many biological transformations are condensation reactions. ], ] synthesis, ] syntheses, ], and ]s are a few examples of this type of reaction. A large number of such reactions are used in synthetic ]. Other examples include:

A large number of such reactions are used in synthetic organic chemistry. Other examples include:


*] *]

Revision as of 03:59, 23 July 2016

The condensation of two amino acids to form a peptide bond (red) with expulsion of water (blue)

A condensation reaction, is a chemical reaction in which two molecules or moieties, often functional groups, combine to form a larger molecule, together with the loss of a small molecule. Possible small molecules that are lost include water, hydrogen chloride, methanol, or acetic acid, but most commonly in a biological reaction it is water.

When two separate molecules react, the condensation is termed intermolecular. A simple example is the condensation of two amino acids to form the peptide bond characteristic of proteins. This reaction example is the opposite of hydrolysis, which splits a chemical entity into two parts through the action of the polar water molecule, which itself splits into hydroxide and hydrogen ions. Hence energy is required to form chemical bonds via condensation.

If the union is between atoms or groups of the same molecule, the reaction is termed intramolecular condensation, and in many cases leads to ring formation. An example is the Dieckmann condensation, in which the two ester groups of a single diester molecule react with each other to lose a small alcohol molecule and form a β-ketoester product.

Dieckmann condensation reaction

Mechanism

Many condensation reactions follow a nucleophilic acyl substitution or an aldol condensation reaction mechanism. Other condensations, such as the acyloin condensation are triggered by radical or single electron transfer conditions.

Condensation reactions in polymer chemistry

In one type of polymerization reaction, a series of condensation steps take place whereby monomers or monomer chains add to each other to form longer chains called polymers. This is termed 'condensation polymerization' or 'step-growth polymerization', and occurs for example in the synthesis of polyesters or nylons. It may be either a homopolymerization of a single monomer A-B with two different end groups that condense or a copolymerization of two co-monomers A-A and B-B. Small molecules are usually liberated in these condensation steps, in contrast to polyaddition reactions with no liberation of small molecules.

In general, condensation polymers form more slowly than addition polymers, often requiring heat. They are generally lower in molecular weight. Monomers are consumed early in the reaction; the terminal functional groups remain active throughout and short chains combine to form longer chains. A high conversion rate is required to achieve high molecular weights as per Carothers' equation.

Bifunctional monomers lead to linear chains, and therefore thermoplastic polymers, but, when the monomer functionality exceeds two, the product is a branched chain that may yield a thermoset polymer.

Applications

This type of reaction is used as a basis for the making of many important polymers, for example: nylon, polyester, and other condensation polymers and various epoxies. It is also the basis for the laboratory formation of silicates and polyphosphates. The reactions that form acid anhydrides from their constituent acids are typically condensation reactions.

Many biological transformations are condensation reactions. Polypeptide synthesis, polyketide synthesis, terpene syntheses, phosphorylation, and glycosylations are a few examples of this type of reaction. A large number of such reactions are used in synthetic organic chemistry. Other examples include:

See named reactions

See also

References

  1. ^ IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (1994) "Condensation Reaction". doi:10.1351/goldbook.C01238
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