Basic IUPAC Organic Nomenclature

Substituted Cycloalkanes

• When the ring size (e.g. number of C atoms) is larger than the longest continuous chain, then the ring becomes the parent and hence the system is treated as a alkyl cycloalkane.

• If a ring is monosubstituted then no locant is required since the substituent must be at C1.
• If a ring is polysubstituted then each substituent requires a locant to unambiguously assign their relative positions.

Ring is smaller than the chain, so the chain is the parent. Functional group is an alkane, therefore suffix = -ane The longest continuous chain is C4 therefore root = but The branch is a C3 cycloalkyl group i.e. a cyclopropyl group The first point of difference rule requires numbering from the right as drawn, the substituent locant is 2-  2-cyclopropylbutane
Ring is larger than the chain, so the ring is the parent. Functional group is an alkane, therefore suffix = -ane The ring is C6 therefore root = cyclohex The branch is a C2 alkyl group i.e. a ethyl group Since it's monosubstituted, no locant is required. ethylcyclohexane
Ring is larger than the chain, so the ring is the parent. Functional group is an alkane, therefore suffix = -ane The ring is C6 therefore root = cyclohex One branch is a C2 alkyl group i.e. an ethyl group The other branch is a C1 alkyl group, i.e. a methyl group Since the first point of difference doesn't resolve the numbering, the alphabetisation order is used. 1-ethyl-2-methylcyclohexane

©Dr. Ian Hunt, Department of Chemistry