Cyclic and Aromatic
Hydrocarbons 
SCH4U Spring 2012
Cyclic Hydrocarbons (Cyclo-)
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Hydrocarbon chains that form rings
Have at least three carbon atoms
Can be alkanes, alkenes and alkynes
General formula for cyclic alkanes: CnH2n
Naming cyclic hydrocarbons
• Identify the root
o Preceded by “cyclo-”
• Identify the suffix
o Not necessary to indicate the location of the double or triple bonds
• Identify the prefix
o If there are no or only one side group on a cyclic alkane, the carbon
atoms are not numbered
o If there are two or more side groups on a cyclic alkane, numbering
must give the lowest possible numbers to all side groups
o If the molecule is a cyclic alkene or cyclic alkyne, the multiple bond
takes highest priority
• Name the compound
Questions
• Name the following:
Questions
• Draw the following:
o 4-ethyl-2-methylcyclopentene
o methylcyclobutane
o 2-ethyl-3-propylcyclohexane
o 1, 2-dimethylcyclohexane
Aromatic hydrocarbons (-benzene)
• Derived from benzene ring (C6H6)
• Aliphatic compounds: do not contain a benzene ring
• Benzene ring:
o All six carbon-carbon bonds are identical in length
o Length of the carbon-carbon bonds is intermediate
between a single and a double bond
o Resonance hybrid
o Delocalized electrons: electrons that make up the
second bond in the “double bonds” are equally shared
by all six carbon atoms
o Conjugated double bonds
o Stable structures
Naming aromatic hydrocarbons
• Identify the root (-benzene)
• Identify the prefix
o prioritize alkyl side groups with six or fewer
carbon atoms in alphabetical order
o Continue to number in the direction of the nearest
side group
• Name the compound (prefix+root)
Naming aromatic hydrocarbons
• If a benzene ring is attached to a single
hydrocarbon chain that has more than six
carbon atoms, the benzene ring becomes a side
group (-phenyl)
Questions
• Name each aromatic hydrocarbon:
Drawing aromatic hydrocarbons
• Draw the benzene ring
• If there is more than one side group, number the
carbon atoms in the ring
• Add the side groups (have six or fewer carbon
atoms)
Questions
• Draw the condensed structural formula for each
aromatic hydrocarbon:
o 1,3-diethyl-4-methyl-2-propylbenzene
o 1-ethyl-3-propylbenzene
• Draw the line structural formula for:
o 2-phenyl-5-propyloctane
o 1,4-dimethylbenzene