Download HYDROCARBONS

HYDROCARBONS
• Hydrocarbons are composed, as their name
suggests mainly of carbon and hydrogen
atoms, though some types have oxygen,
nitrogen or sulphur atoms.
• Hydrocarbons are divided into two groups,
Aliphatics or Aromatics. Most hydrocarbons
are aliphatics.
Representing Hydrocarbon
• There are four ways in which hydrocarbons
can be represented.
• 1. Chemical Formula We are used to using
chemical formulas to represent compounds.
Unfortunately, chemical formulas are not
useful when dealing with organic molecules
because the arrangement of the atoms within
the molecule is important. This can be seen
with the sugars glucose and fructose.
Comparison of glucose and fructose
• 2. Structural formulas are very useful and
important in organic chemistry. A structural
formula shows both the type and
arrangement of the elements and all bonds.
• 3. Condensed formulas show major bonds but
normal C to H bonds are not drawn.
• CH3CH2CH2CH2CH3
• 4. Line diagrams represent the molecule using
lines. The end of a line means CH3 while a
corner is CH2
ALKANES
• Alkanes area class of HYDROCARBONS which contain
only carbon and hydrogen. Two other terms which
describe alkanes are saturated and paraffins.
• Alkanes are SATURATED which means that each carbon
is bonded to four other atoms through single covalent
bonds. Hydrogen atoms usually occupy all available
bonding positions after the carbons have bonded to
each other.
• PARAFFINS which is derived from a Latin word
meaning "little activity", and means that the
compounds are very unreactive.
• The general structure is CnH2n+2
Two common alkanes
Properties
Physical Properties
• Boiling points depend on
chain length. The longer the
chain the higher the boiling
temperature
• Non polar
• Insoluble in water
Chemical Reactivity
• No functional groups,
saturated, and class name
of paraffins which means Unreactive to other
chemicals.
• All compounds: Combustion
Reaction
ROOT ALKANE NAMES
• Root names give the number of carbons in the
longest continuous chain. Root names are used
with various "endings" to indicate branches, type
of bonds between carbons, and functional
groups.
• The following list gives the most basic root the
with normal hydrocarbon alkane endings for the
number of carbons in the longest continuous
chain. Memorize this list.
• Example: root = "eth" + alkane ending = "ane" =
ethane
No. of
Root Name
Carbons
Formula
CnH2n+2
Structure
1
methane
CH4
CH4
2
ethane
C2H6
CH3CH3
3
propane
C3H8
CH3CH2CH3
4
butane
C4H10
CH3CH2CH2CH3
5
pentane
C5H12
CH3CH2CH2CH2CH3
No. of
Formula
Root Name
Carbons
CnH2n+2
Structure
6
hexane
C6H14
CH3CH2CH2CH2CH2CH3
7
heptane
C7H16
CH3CH2CH2CH2CH2CH2CH3
8
octane
C8H18
CH3CH2CH2CH2CH2CH2CH2CH3
9
nonane
C9H20
CH3CH2CH2CH2CH2CH2CH2CH2CH3
10
decane
C10H22
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
Cycloalkanes
• Cycloalkanes contain a carbon chain that is in
the form of a ring. Each cycloalkane has a
formula that is 2H less than the corresponding
alkane. For example, propane is C3H8 whereas
cyclopropane is C3H6. Butane is C4H10 and
cyclobutane is C4H8. The names of the cyclic
structures use the prefix cyclo in from of the
alkane name for the carbon chain.
Timberlake LecturePLUS 1999
13
Cycloalkanes
Cyclopropane
CH2
CH2
CH2
Cyclobutane
Timberlake LecturePLUS 1999
CH2
CH2
CH2
CH2
14
More Cycloalkanes
Cyclopentane
CH2
CH2
CH2
CH2
CH2
Cyclohexane
CH2
CH2 CH2
CH2 CH2
CH2
Timberlake LecturePLUS 1999
15
Naming Cycloalkanes with
Side Groups
Number of
side groups
One
Two
Naming
Side group name goes in front
of the cycloalkane name.
Number the ring in the direction
that gives the lowest numbers
to the side groups and add the
number to the name.
Timberlake LecturePLUS 1999
16
Cycloalkanes with Side Groups
CH3
methylcyclopentane
CH3
CH3
1,2-dimethylcyclopentane
CH3
CH3
1,2,4-trimethylcyclohexane
CH3
Timberlake LecturePLUS 1999
17
ISOMERS
• Isomers are compounds which have the same
formula but have different forms. Some
isomers are known as Structural Isomers
because they have a completely different
atomic arrangement, while others are called
Geometric Isomers because of the spacial
arrangement.
Isomers of C4H10
Butane
2-Methylpropane
Reaction of Alkanes
• Alkanes are very unreactive in most cases. The
exceptions are Combustion and Halogenation.
• Alkanes readily react with oxygen in
combustion reactions to form carbon dioxide
and water. The shorter chain alkanes are the
ones which we normally think of as fuel such
as Methane (natural gas), propane for bbqs,
butane for lighters and octane for the car.
• Halogenation involves the reaction of the
alkane with a halogen such as F2, Cl2, Br2, or I2.
• The product is an alkyl halide in which a H is
replaced by a halogen atom. If the halogen is
in excess the reaction contiunes until all H are
replaced.
• CH4 + F2 → CH3F + HF Fluromethane
• CH3F + F2 → CH2F2 + HF Difluoromethane
• CH2F2 + F2 → CHF3 + HF Trifluoromethane
• CHF3 + F2 → CF4 + HF carbon tetrafluoride