AROMATIC HYDROCARBONS
*Aromatic hydrocarbons are compounds with a structure based on the _____________ ring. Benzene,
C6H6, is colourless, flammable, toxic and carcinogenic, and has a pleasant odour. It is widely used in
the manufacture of plastics, dyes, synthetic rubber, and drugs. (…and used to be added to Perrier
water!)
Representing benzene:
i)
ii)
*iii)
*The Structure of Benzene
*Legend has it that the chemical structure of benzene came
to the German chemist, Friedrich Kekule, in a rather bizarre
dream (see Figure 3 on p. 29). The benzene ring was
originally thought to be composed of alternating carboncarbon ____________ and ____________ bonds, as depicted in
part i) of the table above. Based on this hypothesis, the
alternating bonds in the benzene ring should have different
bond lengths (C-C double bonds are shorter than C-C single
bonds). Upon further analysis, however, it was determined that the six C-C bonds in the benzene ring were
actually all the _________ length; that is, the six C-C bonds in the benzene ring are _____________. These bonds
have an intermediate length, somewhere between the lengths of a C-C single bond and a C-C double bond.
The 18 valence electrons of the benzene ring are thought to be shared equally amongst all the carbons in the
ring. These electrons are said to be __________________ .
Examples: Isomers of Dimethylbenzene (common name = Xylene)
Name
Drawing
The Phenyl Branch
*When naming aromatic hydrocarbons, it is sometimes easier to treat benzene as a branch. If this is the case,
benzene is renamed ________________.
Examples:
*Draw the following compounds:
i) 3-phenylhexane
ii) 4,6-diphenyloct-2-ene
REACTIONS OF HYDROCARBONS
A. Reactions of Alkanes
*Alkanes are ____________________ hydrocarbons. Single covalent bonds are relatively _________ to break,
therefore, alkanes are rather _____________. However, they do undergo ______________ reactions when ignited in
air. This makes them useful ____________. Also, alkanes will react with fluorine (F 2), chlorine (Cl2) or bromine
(Br2) in what are called __________________ reactions. In order for this type of reaction to proceed, however, the
halogen must be exposed to _______and___________________ light.
Examples:
1. a) COMPLETE Combustion of Alkanes
*Recall  Combustion involves a reaction with ___________.
b) INCOMPLETE Combustion of Alkanes…occurs when the supply of oxygen is not plentiful
2. Substitution (…. of a ______________ atom with a _____________ atom)
B. Reactions of Alkenes and Alkynes
*Alkenes and alkynes are ___________________hydrocarbons. The presence of ________________ and
__________________ bonds makes them much more reactive than ___________________. Alkenes and
alkynes undergo ________________ reactions. This type of reaction involves the addition of atoms to
the hydrocarbon molecule without the loss of ____________________. The four types of addition
reactions that will be examined include: halogenation, hydrogenation, hydrohalogenation, and
hydration.
Examples of Addition Reactions involving Alkenes:
Type of Add’n Reaction
1. Halogenation
2. Hydrogenation
*3. Hydrohalogenation
*4. Hydration
Example
*Markovnikov’s Rule
Complete the following: (propene + hydrogen chloride gas)
+ HCl(g) 
or
*Which one predominates? Markovnikov’s rule is often referred to as the “rich get richer” rule.
That is, the carbon within the ___________________ bond that already has more _______________,
bonds to the hydrogen from the hydrohalogen (or water). In other words, the carbon that already
has more hydrogen gets “richer” in _____________________.
C. Reactions of Aromatic Hydrocarbons
Reactivity of hydrocarbons: *alkynes > alkenes > aromatics > alkanes
*As you can see from this progression, aromatic compounds are less reactive than alkynes and
alkenes, but more reactive than alkanes. Aromatics undergo ____________________ reactions; they do
not undergo _______________ reactions.
Examples:
i) benzene + Cl2:
ii) benzene + nitric acid:
iii) benzene + alkyl halide:
PROPERTIES OF ALKANES
A. ALKANES
*Since the electronegativities of carbon and hydrogen are very similar, bonds between C and H are relatively
__________________. As a result, aliphatics are said to be __________________ molecules. The intermolecular
forces that exist between adjacent nonpolar molecules are relatively weak. These forces are called
_______________ ___________________ forces.
*Observe the following data and then complete the activity below the table.
Name
Formula
Molar Mass
(g/mol)
Melting Point
(°C)
Boiling Point
(°C)
methane
CH4
16
-182
-161
ethane
C2H6
30
-183
-89
propane
C3H8
44
-187
-44
butane
C4H10
58
-138
-0.5
pentane
C5H12
72
-130
36
hexane
C6H14
86
-95
68
heptane
C7H16
100
-91
98
octane
C8H18
114
-57
125
nonane
C9H20
128
-54
151
decane
C10H22
142
-30
174
1. Briefly summarize and explain the trend in melting/boiling point.
2. Explain the process referred to as fractional distillation. (See p. 15 of text)
3. List some uses of alkanes. (See table 3 on p. 16 of text)
# of
Structural
Isomers
1
1
1
2
3
5
9
18
35
75