12.10: Drawing and Naming Cycloalkanes

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Learning Objectives

To name cycloalkanes given their formulas and write formulas for these compounds given their names.

The cycloalkanes—cyclic hydrocarbons with only single bonds—are named by adding the prefix cyclo- to the name of the open-chain compound having the same number of carbon atoms as there are in the ring. Thus the name for the cyclic compound C₄H₈ is cyclobutane. The carbon atoms in cyclic compounds can be represented by line-angle formulas that result in regular geometric figures. Keep in mind, however, that each corner of the geometric figure represents a carbon atom plus as many hydrogen atoms as needed to give each carbon atom four bonds.

Some cyclic compounds have substituent groups attached. Example \(\PageIndex{1}\) interprets the name of a cycloalkane with a single substituent group.

Example \(\PageIndex{1}\)

Draw the structure for each compound.

cyclopentane
methylcyclobutane

Solution

The name cyclopentane indicates a cyclic (cyclo) alkane with five (pent-) carbon atoms. It can be represented as a pentagon.

The name methylcyclobutane indicates a cyclic alkane with four (but-) carbon atoms in the cyclic part. It can be represented as a square with a CH₃ group attached.

Exercise \(\PageIndex{1}\)

Draw the structure for each compound.

cycloheptane
ethylcyclohexane