Haloalkanes
Naming haloalkanes: Practice exercises
How to name haloalkanes (alkyl halides): fluoro, chloro, bromo and iodo prefixes, numbering and alphabetical order, with exercises and worked answers.
In a haloalkane (alkyl halide) one or more hydrogens of an alkane are replaced by fluorine, chlorine, bromine or iodine. In a systematic name the halogen is always a prefix: fluoro-, chloro-, bromo-, iodo-. It is treated exactly like an alkyl group.
The rules you need
- The parent is the longest carbon chain, as for an alkane; the halogens are substituents on it.
- Number the chain to give all substituents together the lowest locants, halogens and alkyl groups alike. If both ends give the same set, the prefix cited first in alphabetical order gets the lower number.
- Cite the prefixes in alphabetical order: bromo, chloro, ethyl, fluoro, iodo, methyl.
- Several identical halogens take di-, tri-, tetra-, and each atom gets its own locant: 1,1,1-trichloroethane has three chlorines on C1.
- Rings: the halogen is a prefix on the cycloalkane: bromocyclohexane, with no locant when it is the only substituent.
You will also meet functional class names, which give the alkyl group and then the halide: ethyl bromide for bromoethane, methyl iodide for iodomethane.
Two names, read step by step
1-Bromo-2-methylpropane
The longest chain has three carbons, with a bromine on an end carbon and a methyl group on the middle one. Numbering from the bromine end gives the locants 1 and 2; from the other end, 2 and 3. The lower set wins, and bromo is cited before methyl.
1-Bromo-4-chlorobutane
A bromine on one end of a butane chain and a chlorine on the other. Both ends give the locants 1 and 4, so the alphabet decides: bromo comes before chloro and gets the 1.
Watch out for
- The halogen has no priority of its own in numbering; only a tie is broken alphabetically.
- A halogen forms one bond, so it always sits at the end of a branch, never inside a chain.
- Primary, secondary and tertiary describe the carbon that carries the halogen: count the carbons bonded to that carbon.
Draw from the name: 17 exercises
Each name opens its exercise. Draw the structure and check it: any correct drawing is accepted, and hints and a worked answer help when you are stuck.
- 2-chloropropane Beginner
- 1-bromobutane Beginner
- iodoethane Beginner
- bromocyclohexane Beginner
- 1,2-dichloroethane Beginner
- 2,2-dichloropropane Beginner
- 2-bromo-2-methylpropane Intermediate
- 1-chloro-3-methylbutane Intermediate
- trichloromethane Intermediate
- 1,1,1-trichloroethane Intermediate
- 2-chloro-2-methylbutane Intermediate
- 1-chloro-2,2-dimethylpropane Intermediate
- 1-bromo-1-methylcyclohexane Intermediate
- 1-bromo-3-chloropropane Advanced
- 3-bromo-2,2-dimethylbutane Advanced
- 1-chloro-3-iodopropane Advanced
- 2-bromo-2-chloro-1,1,1-trifluoroethane Advanced
Name the structure
17 structures of this family to name, each with four names to choose from and an explanation of every wrong choice.
Printable worksheet
For practice on paper: names to draw and structures to name, with an answer key to check your work.
The full guide
The guide Haloalkanes explains these names in more detail, with more worked examples and the most common mistakes.