Properties of Alkanes
Long, unbranched alkanes tend to have higher melting
points, boiling points, and enthalpies of vaporization than
their branched isomers
Cycloalkanes: ring alkanes; made up of CH2 groups
General formula: CnH2n
cyclohexane
“boat”
“chair”
Unsaturated Aliphatic Hydrocarbons
Alkenes: carbon-carbon double bond (sp2 hybridized)
Alkynes: carbon-carbon triple bond (sp hybridized)
CHCH
(acetylene)
CH2=CH2
(ethylene)
IUPAC Nomenclature for Aliphatic Hydrocarbons
Straight-chain alkanes - name ends in -ane
Branched alkane - side chain is a “substituent”
 name the substituent formed by the removal of one H atom
from an alkane by changing the ending from -ane to -yl
 name of the alkane is derived from the longest continuous
carbon chain
 to indicate the position of the substituent, the C atoms in
the longest chain are numbered, starting at the end that will
give the lowest number for the position of the first attached
group
 use prefixes di-, tri-, tetra-, penta-, etc. to indicate the
number
 substituents are listed in alphabetical order (disregard the
prefix)
CH3
H 3C
CH
5
4
CH3
CH2
3
C
2
CH3
2,2,4-trimethylpentane
1
CH3
H 3C
CH3
CH2 CH3
2-ethyl-1,1-dimethylcyclohexane
(sum of the numbers is lowest)
Alkenes and Alkynes
Double bonds - change the “ane” suffix to “ene”
Triple bonds - change the “ane” to “yne”
Position of the multiple bond is given by the number of the
first C atom in the multiple bond
CH3-CH2-CH=CH-CH3
2-pentene
CH3-CH2-CH2-CCH3
1-pentyne
CH2=CH-CH=CH2
1,3-butadiene
Reactions of Alkanes
Alkanes are not very reactive
Strong C-C and C-H bonds
mean bond enthalpy (kJ/mol)
C-C
348
C-H
412
1) Oxidation Reactions
CH4(g) + 2 O2(g)  CO2(g) + 2H2O(g)
DHo = -890 kJ
Break the strong C-H bond, but replaced by two C=O bonds
(mean bond enthalpy of C=O is 743 kJ/mol). Also O-H bond is
strong (463 kJ/mol)
2) Substitution Reactions
light or heat
CH4(g) + Cl2(g)
CH3Cl(g) + HCl(g)
light or heat
Cl-Cl
2 Cl
Cl + CH4  CH3 + HCl
initiation step
propagation steps
CH3 + Cl2  CH3Cl + Cl
Cl + Cl  Cl2
CH3 + CH3  CH3CH3
CH3 + Cl  CH3Cl
termination steps
Alkenes
Prepration - Elimination Reactions
1) From alkanes by dehyrogenation
CH3CH3(g)
catalyst
CH2=CH2(g) + H2(g)
2) From haloalkanes - dehydrohalogenation
CH3CH2Cl + KOH  CH2=CH2 + KCl + H2O
H2C
Cl
CH2
+
K
OH
H2C
CH2 +
KCl + H2O
H
3) Dehydration of alcohols
CH3CH2OH
H2SO4
CH2=CH2(g) + H2O
http://www.whfreeman.com/chemicalprinciples/con_index.htm?18
Reactions
1) Addition reactions
Double bonds are more reactive than single bonds
Br
C
C
+ Br
Br
CCl4
C
C
Br
C
C
+
H
H
catalyst
C
C
H
H
http://www.whfreeman.com/chemicalprinciples/con_index.htm?18
H 3C
CH2
CH2 Cl
1-chloropropane
H
H
C
H 3C
+ HX
C
H
H 3C
CH
CH3
Cl
2-chloropropane
2-chloropropane is the product
The H atom always goes to the C atom of the double bond
that already has the most H atoms - Markovnikov addition
H 3C
CH2
CH2 OH
1-propanol
H
H
C
H 3C
C
+ HOH
H
H 3C
CH
CH3
OH
2-propanol
Markovnikov’s rule holds - 2-propanol is favored
Polymerization reactions
n CH2=CH2
catalyst
-[CH2-CH2]-n
CH3
H 2C
CH3
C
H 2C
CH
C
CH2
CH
CH2
isoprene
(2-methyl-1,3-butadiene)
H 3C
H
C
H 2C
n
H 3C
C
H
C
H 2C
H 3C
C
C
H2
H
C
H 2C
C
H2
rubber
cis geometry
C
CH2
H2
C
H3 C
C
H2 C
CH2
C
C
H H3 C
H H3 C
C
H2 C
CH2
C
C
H2
gutta-percha
trans-geometry
C
H
Aromatic Hydrocarbons
Parent compound of aromatic hydrocarbons - benzene (C6H6)
C is sp2 hybridized, ring is planar
As a substituent - phenyl (C6H5)
OH
Phenol (C6H5OH)
CH3
CH3
O2 N
NO2
NO2
Toluene
2,4,6-trinitrotoluene (TNT)
Resonance Stablization
p-bonding electrons are delocalized over all C atoms
Resonance imparts stability to benzene with respect to
hydrogenation and oxidation
cyclohexane
Addition (Br2)
none
cyclohexene
rapid
benzene
none
Substitution Reactions - p-bonds in the ring are left intact;
substituent replaces an H atom
Br
+ Br 2
FeBr3
+
HBr
NO2
Nitration
+
HNO 3
H2SO4
+
H 2O
+
H 2O
SO3 H
Sulfonation
+
H 2SO4
SO3
Akylation
CH3
+
CH3Br
AlBr3
+
HBr