Chemistry » Organic Molecules » IUPAC Naming And Formulae

Naming Alkyl Halides

Naming alkyl halides

All the same rules apply when naming the alkyl halides as for naming the hydrocarbons. We will only be dealing with the haloalkanes (i.e. there are no other functional groups). The halogen atom is treated in the same way as a branched group.

Example: Naming the Haloalkanes

Question

Give the IUPAC name for the following compound:

Naming Alkyl Halides

Identify the functional group

There is a halogen atom and no other functional group. This compound is therefore a haloalkane, and will have the suffix -ane.

Find the longest carbon chain containing the functional group

There are three carbons in the longest chain containing the halogen atom. The prefix is prop-.

Number the carbon atoms in the longest chain

You need to number the carbon atoms so that the halogen atom is on the carbon atom with the lowest number. In this case you can number from either side.

Name the halogen atom and assign the number for the carbon atom it is attached to

The halogen is a chlorine atom. It is attached to carbon number 2 and so will have the name 2-chloro.

Look for branched groups

There are no branched groups in this compound.

Combine the elements of the name into a single word in the following order: halogen atoms; prefix; name ending according to functional group

The name of the compound is 2-chloropropane.

Example: Naming the Haloalkanes

Question

Give the IUPAC name for the following compound:

Naming Alkyl Halides

Identify the functional group

There are three halogen atoms and no other functional groups. This compound is therefore a haloalkane, and will have the suffix -ane.

Find the longest carbon chain containing the functional group

There are four carbons in the longest chain containing all the halogen atoms. The prefix for this compound will be but-.

Number the carbon atoms in the longest chain

You need to number the carbon atoms so that the halogen atoms are on the carbon atoms with the lowest numbers. You must number from left to right here so that one halogen atom is on carbon 1 and two halogen atoms are on carbon 3.

Name the halogen atoms and assign the number for the carbon atom attached to it

There are two halogen atoms that are bromine atoms and one that is fluorine. One bromine is attached to carbon 1 and one is attached to carbon 3. The fluorine atom is attached to carbon 3. So you have 1,3-dibromo- and 3-fluoro.

Look for branched groups

There are no branched groups in this compound.

Combine the elements of the name into a single word in the following order: halogen atoms in alphabetical order; prefix; name ending according to functional group

The name of the compound is 1,3-dibromo-3-fluorobutane. Note that we place the halogens in alphabetical order: bromo (ignore the di/tri/tetra) is before fluoro.

Example: Naming the Haloalkanes

Question

Draw the structural and condensed structural formula for the organic compound

2-iodo-3-methylpentane

Identify the functional group

This compound has the suffix -ane, but also contains a halogen atom. It is therefore a haloalkane. Note that the methyl and iodo are written in alphabetical order.

Find the longest carbon chain containing the functional group

The prefix is pent- therefore there are 5 carbons in the longest chain.

Naming Alkyl Halides

Place the halogen atom(s) and any branched groups

There is an iodine atom on the second carbon atom, and a methyl branched group on the third carbon atom.

Naming Alkyl Halides

Combine this information to and add the hydrogen atoms

Naming Alkyl Halides

Condense the structural formula

First condense the main chain: \(\text{CH}_{3}\text{CHCHCH}_{2}\text{CH}_{3}\)

Then add the side chains and halogen atoms (in brackets) on the relevant carbon atoms: \(\text{CH}_{3}\text{CH}(\text{I})\text{CH}(\text{CH}_{3})\text{CH}_{2}\text{CH}_{3}\)

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