Aromatics
Aromatic Hydrocarbons: hydrocarbon based on the aromatic benzene ring (C 6H6)
or



Benzene is shown to have three single bonds and three double bonds
In reality the 18 electrons are shared across the whole six-sided molecule
Six identical bonds, each one is half way between a single and double bond which
increases the stability of the structure
Examples
NO2
HC=CH2
a)
CH3 b)
c)
NO2
NO2
CH3
methylbenzene phenylethene
(toluene)
2,4,6-trinitromethylbenzene
(styrene)
(trinitrotoluene, TNT)
Rules for naming Aromatic Hydrocarbons
1.
2.
3.
4.
number benzene ring starting with most complex group
name branches attached to the benzene ring, start so that the lowest possible numbers are
used
branch numbers and names are prefixes to benzene root
if branch is complex, use it as the root and name the benzene ring as a branch, called a phenyl
group
Reactions of Hydrocarbons
Combustion: all hydrocarbons burn
Substitution Reactions:
 characteristic of alkanes
 C-C bond difficult to break
 hydrogen atoms can be substituted by halogen atoms to produce alkyl halides
 reaction can continue, further chlorination
Addition Reactions:




characteristic of alkenes and alkynes
much more reactive (don’t need heat or light)
molecules are added to compound, no loss of hydrogen
double/triple bonds are broken, new bonds formed
Addition Reactions
 Halogenation (Br2, Cl2)
CH3 – CH = CH2 +

 Hydrogenation (H2)
CH3 – CH = CH2 +

 Hydrohalogenation (hydrogen halides)
CH3 – CH = CH2 +

 Hydration (H2O)
CH3 – CH = CH2 +

Markovnikov’s Rule: When two different atoms are added, the
hydrogen bonds with the carbon that is already bonded to the most
hydrogen atoms.
 Substitution (halogen)
CH3 – CH2 – CH3 +
