Carbon Chemistry

Carbon can form four bonds. As a result, carbon forms a variety of structures and is therefore the
building block to life on this planet. Hydrocarbon means the compound contains hydrogen and
carbon. Carbon can form:
• straight chains

As a result carbon forms many three dimensional compounds.

Naming of the Alkalies, Alkenes, Alkynes and Alcohol Families
To name alkanes, alkene and alkynes we need to recognise that these carbon families form a
homologous series. Also the number of carbon atoms present is given a prefix specific to that number:

Prefix	Number of carbon atoms
Meth-	1
Eth-	2
Prop-	3
But-	4
Pent-	5
Hex-	6
Hept-	7
Oct-	8
Non-	9
Dec-	10

Alkanes
The general formula for naming alkanes is:
C_nH_2n+2
where n represents the prefix number. For example, for the prefix prop, n=3:
C₃  H_{(2×3) +2}
= C₃H₈
To name this alkane add -ane to the prefix, i.e. propane.

Alkenes
The general formula for naming alkenes is:
C_nH_2n
where n represents the prefix number. For example, for the prefix but, n=4:

C₄H_2×4
= C₄H₈

To name this alkene add -ane to the prefix, i.e. butene.

Alkynes
The general formula for naming alkynes is:
C_nH_2n-2
where n represents the prefix number. For example, for the prefix pent, n=5:

C₅H_{(2×5) – 2}
C₅H₈

To name this alkene add -yne to the prefix, i.e. pentyne.

Alcohols
The naming of alcohols follow the same pattern as the other homologous series. It is important to note that the prefixes are different and the alcohols end in -ol.

Prefix	Alkyl Group
Methyl-	CH3–
Ethyl-	C2H5–
Propyl-	C3H7–
Butyl-	C4H9–
Pentyl-	C5H11–
Hexyl-	C6H13–
Heptyl-	C7H15–
Octyl-	C8H17–
Nonyl-	C9H19–
Decyl-	C10H21–

To name an alcohol:

1. Select the prefix.
2. Add the -el, with alcohol. e.g. Methyl alcohol or Methanol
   Ethyl alcohol or Ethanol Chemical and Structural Formula of Alkanes, Alkenes, Alkynes and Alcohols
   
   Homologous Series Naming:
3. These carbon compounds form with bonds between carbon and hydrogen

Alkanes:
These carbon compounds form with single bonds
between carbon and hydrogen.

Name	Formula	Number of C atoms	Structure
Methane	CH4	1
Ethane	c2H6	2
Propane	C3H8	3

Alkenes:
Like the alkanes these form with carbon and hydrogen but they contain double bonds.
Methene with 1 C atom does not exist as a stable molecule

Name	Formula	Number of C atoms	Structure
Ethene	C2H2	2
Propene	C3H8	3
Butene	C4H8	4

Alkanes:
These carbon compounds form with single bonds
between carbon and hydrogen.

Name	Formula	Number of C atoms	Structure
Ethyne	c2H2	2
Propyne	C3H4	3
Butyne	C4H6	4

The alcohols are a carbon-hydrogen chain but also contain an -OH group.
This OH group is the alcohol group.

120 Name	Formula	Number of C atoms	Structure
Methanol	CH3OH	1
Ethanol	C2H5OH	2
Propanol	C3H7OH	3

Chemical and Physical Properties of Alkanes, Alkenes, Alkynes and Alcohols
The physical properties of alkanes, alkenes, alkynes and alcohols are summarised in the following table:

Homologous Series	Properties
Alkanes	Insoluble in water. Less dense than water
Alkenes	Insoluble in water. Boiling and melting points increase with size of the molecule. Smaller molecules are gases and the larger are solids.
Alkynes	Insoluble in water. Boiling and melting points increase with size of the molecule. Smaller molecules are gases and the larger are solids.
Alcohols	Alcohols have a neutral pH. Alcohols are soluble in water. Larger molecules are less soluble.

Alkanes generally burn very well in air and as a consequence are used as fuels. The burning of alkanes
can generate considerable heat.

Combustion Reactions:

Plentiful Supply of air:
Ethane + Oxygen Carbon dioxide Water
2C2H6 + 702 ---> 4C02 + H2O

Limited supply of air:
Ethane + Oxygen - - Carbon monoxide Water
2C2H6 + 502 ---> 4C02 + H₂O
Very limited supply of air:
Ethane -I- Oxygen - Carbon monoxide Water
2C2H6 + 302 ---> 4C + 6H2O

NB: The carbon appears as black soot.

Aikenes
The burning of alkenes produces a sooty, more orangy-yellow flame than the alkanes. Alkenes can also
bum both incompletely and completely.
e.g. Complete combustion:

Ethene • Oxygen •-•+- Carbon dioxide ± Water
C₂H₄ +30₂ —–> 2CO_{2 +} 2H₂O

Triple Bond between the two C atoms.

The yellow-orange flame if apparent is due to the presence of carbon particles in the flame.

Alkynes
The most well known alkyne is acetylene (ethyne). This is used in oxy-acetylene welders to produce
intense heat. The energy from the heat is produced when the alkynes C-C triple bond breaks.
e.g.
Ethyne + Oxygen —> Carbon dioxide + Water
2C₂H₂ + 50₂ —> 4CO_{2 +} 2H₂0 (and Intense Heat)

Alcohols
Alcohols are combustible. The most relevant example of the combustion of alcohols is ethanol.
Petrol can produce carbon monoxide and carbon, whereas ethanol is clean burning to carbon
dioxide and water.

Ethanol + Oxygen —-> Carbon dioxide + Water
C₂H₅OH + 30₂ —–> 2CO₂ + 3H₂0

The reaction produces heat energy. This makes it suitable as a bio-fuel alternative to fossil fuels such as petrol.

Plastics from Alkenes

Plastics from Alkenes
Alkenes are the building blocks for plastics. Each individual alkene molecule’s double bond can break
and link to another molecule, This process is called polymerisation.

NB: then represents a repeating chain of n units.

One alkene molecule is called a monomer. The long chain of monomers is called a polymer, i.e. mono
means one, and poly means many.

The reaction with ethene is with n number of ethyne molecules:

When many chains are layered alongside each other a plastic sheet fors

This type of reaction with different monomers as starting units forms the basis of all our plastics.