Question

How do you name cycloalkanes with double bonds?

Answer 1

Cycloalkanes with double bonds are known as cycloalkenes, and have nomenclature as a combination of cyclic molecules and alkenes.

Explanation:

Nomenclature is naming.

Nomenclature of cyclic or circular molecules involves counting the number of carbon atoms and giving it the appropriate root (e.g. 6 `->` 'hex-', 4 `->` 'but-') and adding 'cyclo-' as a prefix.

For example, a circular molecule with five carbon atoms and two double bonds between carbon numbers 1-2 and 3-4 would be

cyclopenta-1,3-diene

The nomenclature of alkenes is fairly straight forward.

root + where DB's are + number of DB's + ene

In the case above, cyclopenta-1,3-diene, 'penta-' is the root, '-1,3-' is where the double bonds are located, '-di-', from the Latin for two, is how many double bonds there are, and '-ene' is the suffix for an alkene.

More examples are

cycloprop-1-ene or simply cyclopropene `->` three carbon atoms in a triangular form, with one double bond on the first carbon.

cyclohepta-1,2,5-triene `->` seven carbon atoms, with three double bonds between atoms 1-2, 2-3 and 5-6 in a heptagon format.

cyclobuta-1,3-diene `->` four carbon atoms with two double bonds between atoms 1-2 and 3-4 in a quadrilateral.