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Hydrocarbons / Organic
Chemistry
Organic Chemistry
• Organic chemistry is the study of the
structure, properties, composition,
reactions, and preparation of the chemical
compounds that contain carbon.
Hydrocarbons
•
Hydrocarbons are molecules which
contain hydrogen and carbon
• There are many different compounds
that can form with carbon and hydrogen
• There are 3 main hydrocarbon families
1. Alkane
2. Alkene
3. Alkyne
Where do you find hydrocarbons?
• Carbon compounds make up 90% of all
chemical compounds and many form the
basis of living systems
• The majority of hydrocarbons found
naturally occur in crude oil
• Crude oil forms from decomposed organic
matter which has lots of carbon and
hydrogen!.
• Proteins, carbohydrates and fats
all contain carbon, hydrogen and
oxygen
What are the differences and
similarities of the compounds below
1. Alkanes
• Are hydrocarbons that contain only carbon
and hydrogen
• They only have single bonds
• CnH2n + 2
• A series of compounds with similar
properties in which each member differs
from the previous one by –CH2 is known as
a homologous series
• Structural formulas show the number and
location of bonds but not lone pairs
Straight and branched chain
• A straight-chain is where the carbon atoms in an
alkane, alkene and alkyne form a chain that runs
from one end of the molecule to the other.
• A branched chain is were an alkane, alkene and
alkyne has alkyl groups bonded to its central
carbon chain.
• An alkyl is a group of atoms consisting of carbon
and hydrogen atoms, arranged in a chain.
Naming carbon compounds
No. of carbon
Atoms
1
2
3
4
5
6
7
8
9
Prefix
MethEthPropButPentHexHeptOctNon-
What are the differences and
similarities of the compounds below
2. Alkenes
• Contains at least one carbon to carbon
double bond
• The alkenes are a homologous series
• CnH2n n = integer
Naming Alkenes
• Carbon atoms are
labelled from left to
right
• Identify where the
double bond starts
• And put that number
between the prefix
and suffix of the
alkene
But-1-ene
But-2-ene
Naming alkenes with 2 double
bonds
• If there are two
double bonds the
suffix (ending) is diene
• 3 double bonds triene
• buta-1, 2-diene
3. Alkynes
• Are hydrocarbons that contain only carbon
and hydrogen
• They have at least one triple bond
• The alkynes are a homologous series
Naming carbon compounds
Suffix
If all of the carbon to carbon
bonds are single
-ane
If there is at least one carboncarbon bond is a double bond
-ene
If there is at least one carboncarbon bond is a triple bond
-yne
Structural isomers
• Structural isomers are molecules with the
same molecular formula but different
arrangement of their atoms (different structural
formulas)
Structural Isomers
Structural isomers
Semi-structural formulas
• Semi- structural formula is a structural
formula without giving the arrangement
atoms in space
Make and then draw as many
isomers of hexane as possible
Naming isomers
1. Name and number longest carbon chain (circle it)
2. Identify branches (there are no branches at ends!)
3. Name each branch (alkyl group) put them in
alphabetical order
• methyl CH3 ethyl C2H5 propyl C3H7 butyl C4H9
pentyl C5H11
4. If there is more than 1 alkyl group use:
di = 2, tri = 3, tetra = 4 as a prefix e.g. diethyl, trimethyl
5. Write the number of the carbon atom each alkyl group
is attached to. Put commas between numbers if there
is more than one alkyl group (2,3-dimethyl)
6. Put hyphens between numbers and words (2,2 –
dimethylbutane)
Name the following
• n
2-methyl propane
propane
Name the following carbon
compounds
5-ethyl-5,6,6-trimethyl
decane
4,5-diethyl-5,6-dimethyl4-propyloctane
Are these
named
correctly?
Rewrite the
names that
are
incorrect
Name all the isomers of hexane you drew
Saturated compounds
• A saturated compound has no double or triple
bonds.
• In saturated linear hydrocarbons, every carbon
atom is attached to two hydrogen atoms, except
those at the ends of the chain, which have three
hydrogen atoms.
• In the case of saturated methane, four hydrogen
atoms are attached to the single, central carbon
atom.
• Of simple hydrocarbons, alkanes are saturated,
and alkenes are unsaturated.
Unsaturated carbon compounds
• Alkenes and alkynes are unsaturated
carbon compounds because they contain
less hydrogen than the maximum amount
possible
Which compound/s are saturated?
• v
Physical Properties of Alkanes
and Alkenes
• As the number of carbon atoms increases
in a homologous series there is a change
in the physical properties
• At room temperature, the lighter alkanes
and alkenes are gases; the midweight
alkanes are liquids; and the heavier
alkanes are solids, or tars.
• Why?
• London forces increase as molecules get
heavier
Boiling Point
• The boiling points of the
alkanes and alkenes
gradually increase with
the molecular weight of
the compounds.
• Alkanes and alkenes
have similar boiling
points
• Alkenes have a slightly
lower
Hydrocarbons Boiling point
(C)
Methane
-161.5
Ethane
-88.6
Propane
-42.1
Butane
-0.5
Pentane
36.1
Volatility
• Volatile liquids are those
that evaporate (go from
liquid to solid) easily.
• Smaller molecules are
more volatile
• Why?
• Because there are weak
London forces so it is
easier for them to go from
a liquid to a gas
Viscosity
• Viscosity is the measure of the thickness of a
fluid
• Honey is more viscose (it is harder to pour)
than water
• The larger the molecule the more viscous it is
• The larger the molecule the stronger the
London forces which means they are more
likely to stick together because they are long
they get tangled up like spaghetti
DONE
Chemical Properties of Alkanes
Chemical Properties of Alkenes
• Alkenes have different chemical properties
to alkanes due to the double bonds in
alkenes
• Alkenes react much more readily than
alkanes
• http://www.sciencegeek.net/APchemistry/
APtaters/alkanes.htm