Addition



Composed by: Alec and Cory toc

=Introduction = An addition reaction, in [|organic chemistry], is one in which two parts of a molecule are added to an unsaturated molecule, increasing the [|saturation] of the molecule. In simpler terms, two or more molecules combine to form a larger molecule. [|Hydrogenation] is a common type of addition reaction where hydrogen atoms are added to an unsaturated molecule. Addition reactions can only occur with chemical compounds that have multiply-bonded atoms, such as carbon-carbon double bonds ([|alkenes]) or triple bonds ([|alkynes]). Among alkenes and alkynes, molecules consisting of [|carbonyl groups] can also partake in an addition reaction.

=Reaction Examples = In organic chemistry, an addition reaction can be illustrated when a simple molecule gets added across a carbon-carbon double bond in an unsaturated compound. An addition reaction only occurs with unsaturated compounds containing double or triple bonds. They can either be the radical addition of a halide to an alkene, [|electrophilic]or [|nucleophilic]. Below is the general formulas for each of the mentioned types of addition reactions. From top to bottom, electrophilic, nucleophilic, and the addition of a halide to an alkene are represented:



﻿Halide to an Alkene
One example of an addition reaction is the radical addition of a halide to an alkene. Below shows an addition reaction between [|chlorine] (Cl2) and [|ethene] (CH2=CH2 ) which produces [|1,2-dichloroethane](ClCH2(CH2)Cl).





Electrophilic Addition Reaction
An electrophilic reaction is an addition reaction where a double bond is broken and two new bonds are formed. Here is an example of a electrophilic addition reaction:

[|Hydrochloric acid] reacts with an alkene, ethene, to produce [|1-chloroethane]: HCl + CH2:CH2 → CH3CH2Cl

For an animation of a different electrophilic addition reaction, refer to the video under the Reaction Mechanism Examples heading.

Nucleophilic Addition Reaction
A nucleophilic addition reaction occurs when a double bond is removed by the creation of two new covalent bonds with the addition of a [|nucleophile].

An example of nucleophilic addition is the addition of hydrogen cyanide across the carbonyl bond in aldehydes to form [|cyanohydrins]. Here, [|ethanal] reacts with [|hydrogen cyanide] to create 2-hydroxypropanenitrile:



A different nucleophilic addition reaction can be shown in the following animation video:

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=Reaction Mechanism Examples =

In this reaction mechanism, ethene is reacting with a bromine molecule. Electrons are leaving the double bond from the ethene and moving to one of the bromine atoms. The electron leaves the bromine-bromine bond and moves to the other bromine atom. The bromine atom then bonds to the original ethene that had lost electrons from the double bond. The remaining bromine atom then bonds to the original ethene that had lost electrons from the double bond which then creates 1,2-dibromoethane. Below is a video of an animation of the reaction shown above:

media type="youtube" key="-t3yEoYcSdI?fs=1" height="385" width="480" align="center"



In this reaction mechanism, ethene is reacting with hydrobromic acid. Electrons are moving from the double bond to the hydrogen atom. The electron leaves the hydrogen-bromine bond and moves to the bromine atom. The hydrogen then is bonded with the original ethene that had lost electrons from the double bond. The bromine atom then bonds with the original ethene that had lost electrons from the double bond as well. This produces 1-bromoethane.

=References =

__ Websites: __ Darling, DAvid. World's of David Darling. Web. 5 Nov. 2010. <[|www.daviddarling.info/encyclopedia/.../addition_reaction.html] >.

TalkTalk. 2010. Web. 5 Nov. 2010. < []>.

N.p., n.d. Web. 9 Nov 2010. <[]>.

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__ Images: __ Structural Representation of ethene and chlorine Addition Reaction: [] Atomic Symbol Representation of ethene and chlorine Addition Reaction: [] Ethene Reaction Diagram with bromine molecule: [] Ethene Reaction Diagram with hydrobromic acid: [] Ethene Reaction with hydrochloric acid: [] Ethanal and hydrogen cyanide Reaction: [] General Formulas for Types: []

__ Video: __ <span style="font-family: Arial,Helvetica,sans-serif;">Electrophilic Reaction: [] <span style="font-family: Arial,Helvetica,sans-serif;">Nucleophilic Reaction: []