Download Compounds of Carbon

Compounds of Carbon
Carbon is an important element as it forms 90% of all chemical compounds and forms the basis of living
systems. The chemistry involving carbon was known as organic chemistry, as this term indicated carbons’
importance in living organisms. Carbon is most commonly found in compounds containing hydrogen, oxygen,
nitrogen, sulfur and chlorine. Proteins, carbohydrates and fats, used by our body contain C, H and O. Proteins
can also contain N, S and others.
Why does Carbon form so many compounds?
As discussed earlier, carbon is an interesting element as it has an electronic configuration of 1s22s22p2. This
means it has 4 valence electrons in its outer shell, which is a half full outer shell. To obtain a full outer shell,
and being a non-metal, it forms covalent bonds by sharing all of its valence electrons. It can form single or
double bonds with other elements.
Hydrocarbons
Hydrocarbons are compounds containing hydrogen and carbon. We commonly find hydrocarbons in the form
of fossil fuels: natural gas, coal and oil. They can be classified into several families, sharing common structures
and properties, as they increase in size. These are known as homologous series’: homo means ‘same’ and
genos means ‘kind’.
Alkanes: The alkane homologous series have a general formula CnH2n+2 “Where n is an integer” (remember to
always specify this!) and begins with methane: CH4 Each next alkane in the series differs by CH2. Crude oil
consists largely of alkanes with n = 5-70.
In alkanes:

Each C has a single covalent bond to 4 other atoms

Each H has single covalent bonds to one C

The atoms are arranged in a tetrahedral manner
It is best to use structural formulae to represent hydrocarbons. Always draw the carbons first, connecting
them into a chain, adding hydrogen and other elements later.
FORMULA
NAME
methane
ethane
propane
butane
pentane
hexane
heptane
octane
nonane
decane
Hydrocarbons can form straight chain molecules which are linear overall, even though each carbon still forms
a tetrahedron in three dimensional space. Branched chain molecules have an overall shape which is not
linear. The fact that the carbons can join together in different shapes results in structural isomers: molecules
with the same molecular formula but different arrangements of their atoms. Structural isomers have similar
chemical properties but different physical properties.
Try drawing two structural isomers for Butane C4H10 (one straight chain, one branched)
Note: Chemical properties are caused by
the reactions of a substance’s electrons
Physical properties describe things we can
simply observe about the substance, like
the melting point/boiling temperature.
C20H42 has 366319 possible isomers!
Alkanes are considered saturated hydrocarbons as each C atom has formed its maximum number of bonds.
There are no other bonds available. So, each carbon only has single bonds to others and they are not very
reactive compounds.
Alkenes: Alkenes have the general formula CnH2n. They begin with C2H4, ethene, and also form a homologous
series with each compound differing by CH2. Alkenes can form isomers and various isomers can even be
present in one sample of a compound with a single molecular formula. Alkenes are considered unsaturated
hydrocarbons: They contain at least one carbon to carbon double bond. They have less than the maximum
possible bonds with hydrogen.
FORMULA
NAME
Ethene
propene
butene
 Draw the isomers of C4H8
Naming Carbon compounds
Naming hydrocarbons is easy if you learn and follow some simple rules:

Learn table 8.4 for the prefixes of all hydrocarbons
(1) For straight chain hydrocarbons, the name of the hydrocarbon ends in:

An alkane (only carbon to carbon single bonds, saturated): ane

An alkene (a carbon to carbon double bond, unsaturated): ene

An Alkyne (a carbon to carbon triple bond, unsaturated): yne
(2) For unsaturated hydrocarbons:

Number all the carbons in the chain. Number the carbons in the direction which means that the first
carbon involved in the double/triple bond will have the lowest possible number. Place this number in
front of the name.
(3) For branched hydrocarbons:

Identify the longest continuous chain of carbon

Identify the name of the hydrocarbon formed by the longest continuous chain of carbon.

Are any single/double/triple bonds present? If so, follow steps outlined at (2)

Identify the alkyl group.
o This is the left over group which replaces a hydrogen on one of the central carbons. Alkyl
groups are named after the alkane from which it formed, minus one H atom which is where it
joins to the longest carbon chain. CH3 is a methyl group, derived from methane CH4, minus a
hydrogen.
o You may need to indicate the position that this group is attached to on the longest carbon
chain. Do this by placing the appropriate number in front of the name.

Overall, place the alkyl group name first, followed by the name of the longest carbon chain.

When two, or more identical branches occur on different carbon atoms, the prefixes di-, tri-, and tetraare used.

When you have a Cl- it becomes chloro, Br- becomes bromo, I- becomes iodo
A number of forces can act in and between hydrocarbon molecules:

The intra-molecular forces are covalent.

Hydrocarbons containing only hydrogen and carbon are considered non-polar molecules. Dispersion
forces act between hydrocarbon molecules, attracting them to each other. The strength of the
dispersion forces increases as the size of the molecules increase, as there are more atoms in each
molecule containing charged particles to attract each other.
In smaller molecules, with less intermolecular dispersion forces, less energy is required to overcome
these forces and the liquids will evaporate easily. These sorts of liquids are known as volatile. These
will also flow freely due to the weak forces in the liquid and are said to have low viscosity. Substances
with high viscosity have a thicker texture, like honey.
Functional Groups
A hydrogen on a hydrocarbon molecule can be replaced by other elements. Doing so can change the
chemical properties of the hydrocarbon as, often, we are changing it from a non-polar molecule to a polar
one. The atom or group of atoms replacing a hydrogen on a hydrocarbon, influencing the properties of
compounds in an homologous series, is known as a functional group. Hydrocarbons containing a particular
functional group can form their own homologous series, with predictable properties.
For example, ethane C2H6 belongs to the alkane homologous series but can be used to derive
molecules belonging to the Alcohol and Carboxylic Acid Homologous series’:
Draw the structural formula of ethane from the semi-structural formula CH3CH3:
Remove a hydrogen and add an –OH to form
Ethanol CH3CH2OH (the “alcoholic content” of
drinks):
This belongs to the Alcohol Homologous series
Functional group= OH (hydroxy)
Remove a hydrogen and add an –COOH to form
Ethanoic acid CH3COOH:
This belongs to the Carboxylic Acid Homologous
series
Functional group= COOH (carboxy)
Alcohols
The molecules in the Alcohol homologous series are known as ‘alkanols’. The stem of their names is derived
from the alkane which has the same number of carbons. The name ends in ‘ol’ which represents the presence
of the hydroxy functional group -OH.
For example, methanol has _____ carbons and an –OH functional group. Draw its structural formula:
(Remember: Alkanes are CnH2n+2 then subtract H and add an OH)
The -OH functional group makes the molecules polar. Dispersion forces continue to act between the
molecules, but Hydrogen bonding becomes more prevalent. Consequently, the attraction between
molecules is stronger than in normal alkanes and this is reflected by a boiling temperature which is higher
than in the corresponding alkane.
Carboxylic Acids
The molecules in the Carboxylic Acid homologous series also have the stem of their name derived from the
alkane which has the same number of carbons. The name ends in ‘anoic acid’ which represents the presence
of the carboxy functional group -COOH.
For example, propanoic acid has _____ carbons and an –COOH functional group. Draw its structural
formula:
(Remember: Alkanes are CnH2n+2 then subtract H and add a COOH)
The -COOH functional group makes the molecules polar. Dispersion forces continue to act between
molecules, but Hydrogen bonding is more prevalent. Consequently, the attraction between molecules is
stronger than in normal alkanes and this is reflected by a boiling temperature which is higher than in the
corresponding alkane.
Even when comparing methane with methanoic acid, it is observed that the molecular size is also
significantly larger, increasing the dispersion forces operating at any one time. Draw their structural
formulae:
Amines
Organic compounds that contain the –NH2 functional group are called amines. Amines are soluble in water
due to the formation of hydrogen bonds. This solubility decreases as the size of the alkyl group becomes
larger. The amines are named by adding amino to the name of the alkane.
 Draw aminomethane and 2-aminobutame