Chemistry [[Module Three]] Haloalkanes: Nucleophilic Substitution

[[Nucleophilic Substitution]]

Haloalkanes: homologous series of compunds with general formula CnH2n+1X where X represents F, Cl, Br and I.

- Halogens are electronegative

- Carbon Halogen bonds are polar

- The electrons in C-X bond are attracted to the halogen atom which gains a slight negative charge

- Therefore the Carbon has a slightly positve charge

- The slightly positive carbon is suceptable from attack by nucleophil

Nucleophile: And electron pair donor

- Nucleophilic attack occurs and the carbon halogen bond breaks, releasing a halide. The halide is replaced by the nucleophile.

- rate of reaction influenced by strength of C-X bond

- C-F bond is very polar but bond is very strong so Flouroalkanes are unreactive

- Chloroalkanes also react slowley

- Bromoalkanes react at a reasonable rate

[[Nucleophilic Substitution Reactions]]

[1. Hydroxide Ions]

- haloalkanes warned with aqueous sodium or potassium hydroxide

- forms alcohols

[2. Cyanide Ions]

- haloalkanes warmed with aqueous/alcholic solution of KCN

- nitriles formed

- carbon chain extended

[3. Ammonia]

- warmed with excess of ammonia

- sealed container

- Primary Amines

- excess of ammonia minimises chance of further reaction.