Haloalkanes

4 Parts:

Nucleophilic Substitution

Elimination

Referencing this Article

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If you aren't sure what a haloalkane is, have a look on the nomenclature page.

Haloalkanes contain a polar bond on the functional group. Because the halogen is electronegative, it becomes δ- and the carbon is positive. This means it is susceptible to nucleophilic attack by ions. The strength of the C - Halogen bond also influences the rate of substitution. The C-F bond requires a quite a bit (484 kJmol-1) of energy to break, however, the C-Br bond is easier to break so the rate of reaction is faster. The mechanism below uses the notation :Nu- to refer to the nucleophile, which can either be OH- or NC-.

The mechanism below shows what happens with ammonia and a haloalkane

The bromine ion and NH₄ join to make NH₄Br, and the final product is an amine

In the first mechanism, the OH ion replaces the Br and forms an alcohol. However, the OH- can also act as a base, where an elimination reaction occurs, as outlined below.

How do you decide whether substitution or elimination is going to happen? There are several factors that will determine what will happen. Have a look at the table below.

If you are not sure about the differences between primary, secondary and tertiary then look at the page alcohols, as the same rules apply.

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Haloalkanes. (2017). In ScienceAid. Retrieved Apr 25, 2024, from https://scienceaid.net/chemistry/organic/haloalkanes.html

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