Haloalkanes

Haloalkanes are alkanes which contain a halogen atom (F, Cl, Br or I). They are immiscible (insoluble in water) because they cannot make hydrogen bonds with water, and the organic (carbon-containing) part of the compound effectively makes them non-polar.

Functional Group

R-X

R = a carbon chain

X = halogen atom

Naming/Nomenclature

• Find the largest carbon chain containing the functional group (-X). Name this chain (e.g. butane = 4 carbons)

• Number the carbons in the longest chain. Use this number to identify where the functional group is (e.g. 2 chloro butane)

• If there are side chains (branching), number these using the same numbering system.

Classification and Enantiomers

We covered classification in spectroscopy, and it is the same as for alcohols.

Stereoisomerism was covered in alcohols, and is the same for haloalkanes.

Preparation

We generally make haloalkanes from alkenes or alcohols:

• addition of HX (e.g. HCl to make a chloroalkane) to an alkene. Markonvikov's Rule often applies
• nucleophilic substitution of an alcohol, usually using SOCl₂ (thionyl chloride)

Reactions

Haloalkanes (especially chloroalkanes) are useful compounds for making other functional groups:

1. MAKING AMINES

Note that the ammonia is dissolved in alcohol. This is to prevent hydroxide ions (in an ammonia solution) making the alcohol, instead of the amine.

2. MAKING ALCOHOLS

This is another type of nucleophilic substitution. A strong base is needed, an KOH is our reagent of choice.

3. MAKING ALKENES

This is an elimination reaction. It uses the same reagent as making alcohols, but under different conditions. Note that we may need Saytzeff's Rule for this: