2. Organic Chemistry & Hydrocarbons
Scientists used to think that only living organisms could
synthesize the carbon compounds found in their cells.
They called the study of these compounds organic
chemistry.
However, Friedrich Wohler (1800s) was able to use
inorganic substances to synthesize urea. ( a carbon
compound found in urine)
Today - Organic chemistry includes the chemistry of
almost all carbon compounds regardless of their origin.
3. Hydrocarbons
There are many more organic compounds than inorganic
compounds
The simplest organic compounds contain only carbon and
hydrogen and are called hydrocarbons.
The two simplest hydrocarbons are methane (CH4) and
ethane C2H6.
Methane is a major component of natural gas and is
formed by the action of bacterial on decaying plants in
swamps and other marshy areas.
Livestock and termites also emit substantial quantities of
methane as a product of digestion.
4. Methane
Carbon has 4 valence electrons and hydrogen has 1, so
the carbon atom can form a single covalent bond with
four hydrogen atoms.
Because carbon has four valence electrons, a carbon
atom always forms four covalent bonds.
5. Ethane
Methane is not typical of the vast majority of organic
compounds, because there isn’t a bond between carbon
atoms in a methane molecule.
Ethane has a carbon-carbon bond. Two carbons atoms
share a pair of electrons. The remaining six valence
electrons form bonding pairs with the electrons from six
hydrogen atoms.
6. Alkanes
The ability of carbon to form stable carbon-carbon bonds
is one reason that carbon can form so many different
compounds.
Alkanes are hydrocarbons in which there are only single
covalent bonds.
In alkanes, all the carbon-carbon bonds are single
covalent bonds and all other bonds are carbon
hydrogen bonds.
The carbon atoms in an alkane can be arranged in a
straight change or in a chain that has branches
Alkenes have the general formula CnH2n + 2 (C2H6)
7. Straight-Chain Alkanes
Ethane is the simplest of the straight-chain alkanes, which
contain any number of carbon atoms, one after the
other in a chain.
Propane (C3H8) has three carbon atoms bonded in a chain
with eight electrons shared with eight hydrogen atoms.
Butane (C4H10) has four carbon atoms bonded in a chain
with 10 hydrogen atoms.
Homologous series – a constant increment of change in
molecular structure from one compound in the series to
the next. (straight-chain alkanes are an example)
8. Straight-Chain Alkanes
First Ten Straight-Chain Alkanes
Name Molecular Structural Formula BP (ºC)
Formula
Methane CH4 CH4 -161.0
Ethane C 2H6 CH3CH3 -88.5
Propane C 3H8 CH3CH2CH3 -42.0
Butane C4H10 CH3CH2CH2CH3 0.5
Pentane C5H12 CH3CH2CH2CH2CH3 36.0
Hexane C6H14 CH3CH2CH2CH2CH2CH3 68.7
Heptane C7H16 CH3CH2CH2CH2CH2CH2CH3 98.5
Octane C8H18 CH3CH2CH2CH2CH2CH2CH2CH3 125.6
Nonane C9H20 CH3CH2CH2CH2CH2CH2CH2CH2CH3 150.7
Decane C10H22 CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3 174.1
9.
10. Naming Alkanes
Every alkane has a name that ends with the suffix –ane.
For the straight-chain alkanes with 1 to 4 carbon atoms,
the official names and the common names are the
same. (Methane, ethane, propane, and butane)
A mixture of Latin and Greek prefixes are used to name
the hydrocarbons having straight chains longer than
four carbon atoms.
The prefixes are pent- 5, hex- 6, hept- 7) oct- 8, etc.
A complete structural formula shows all the atoms and
bonds in a molecule. Sometimes, shorthand structural
formulas work just as well.
11. Condensed Structural Formulas
In a condensed structural formula, some bonds and/or
formula
atoms are left out of the structural formula. (even
thought the bonds and atoms do not appear, you must
understand that they are there)
C4H10
CH3 – CH2 – CH2 – CH3
CH3(CH2)2CH3
C–C–C-C
12. Branched-Chain Alkanes
Because a carbon atoms form four covalent bonds, it can
bond not only to one or two other carbon atoms, but also
to three or even four other carbons, resulting in branched
chains.
Branches on a hydrocarbon chain are discusses as if they
were substituted for a hydrogen atom on the chain.
A atom or group of atoms that can take the place of a
hydrogen atom on a parent hydrocarbon molecule is
called a substituent.
The longest continuous carbon chain of a branched-chain
hydrocarbon is called the parent alkane.
All other carbon atoms or groups of carbon atoms are
regarded as substituents.
13. Branched-Chain Alkanes
Substituent C
|
C -- C – C Parent alkane (propane)
Substituents
C C C
| | |
Parent alkane (hexane) C --- C -– C -– C –- C --- C
14. Alkyl Groups
A hydrocarbon substituent is called an alkyl group.
group
An alkyl group can be one carbon or several carbons long.
Alkyl groups are name by removing the –ane ending from
the parent hydrocarbon name and adding –yl.
The three smallest alkyl groups are
• methyl group (CH3 --)
• ethyl group (CH3CH2 --)
• propyl group (CH3CH2CH2 --)
An alkyl group consists of an alkane with one hydrogen
15. Naming Branched-Chain Alkanes
When a substituent alkyl group is attached to a straight-
chain hydrocarbon, branches are formed.
An alkane with one or more alkyl groups is called a
branched-chain alkane.
alkane
The name of a branched-chain alkane is based on the
name of the longest continuous carbon chain.
Each alkyl substituent is named according to the length of
its chain and numbered according to its position on the
main parent chain.
17. Naming Branched-Chain Alkanes
1. Find the longest chain of carbon atoms (parent)
2. Number the carbons in the main chain in sequence. (Start at
the end that will give the groups attached to the chain the
smallest numbers.)
3. Add numbers to the names of the substituent groups to
identify their positions on the chain. (these numbers become
prefixes to the name of the alkyl group)
4. Use prefixed to indicate the appearance of the same group
more than once in the formula. (di-, tri-, tetra-, penta-)
5. List the names of alkyl substituents in alphabetical order.
(ignore the prefixes di-, tri-, etc.)
6. Use proper punctuation. Commas are used to separate
numbers. Hyphens are used to separate numbers and
words. Entire name written without any spaces.
18. Properties of Alkanes
The electron pair in a carbon-hydrogen or a carbon-
carbon bond is shared almost equally by the nuclei of
the atoms form the bond.
Molecules of hydrocarbons, such as alkanes, are nonpolar
molecules.
The attractions between nonpolar molecules are weak van
der Waals forces, so alkanes of low molar mass tend to
be gases or liquids that boil at a low temperature.
The nonpolar hydrocarbon compounds will not form
solutions with polar compounds.
20. Alkenes
Organic compounds that contain the maximum number of
hydrogen atoms per carbon atom are called saturated
compounds. (alkanes)
Compounds that contain double or triple carbon-carbon
bonds are called unsaturated compounds.
compounds
Alkenes are hydrocarbons that contain one or more
carbon-carbon double covalent bonds.
At least one carbon-carbon bond in an alkene is a double
covalent bond. Other bonds may be single carbon-
carbon and carbon-hydrogen bonds.
Alkenes have the general formula CnH2n (C2H4)
21. Naming Alkenes
Ethene (common name ethylene) is the simplest alkene.
To name an alkene by the IUPAC system:
1. Find the longest chain in the molecule that contains the
double bond. (this will be the parent chain). It has the
root name of the alkane with the same number of
carbons plus the ending -ene.
2. The chain is numbered so that the carbon atoms of the
double bond have the lowest possible numbers.
3. Substituents on the chain are name and numbered in
the same way they are for the alkanes.
23. Alkynes
Hydrocarbons that contain one or more carbon-carbon
triple covalent bonds are called alkynes.
Alkynes have the general formula CnH2n-2 (C2H2)
The simplest alkyne is the gas ethyne, which has the
common name acetylene.
Straight chain and branched chain alkanes, alkenes, and
alkynes are aliphatic hydrocarbons.
The major attractions between aliphatic molecules are
weak van der Waals forces. (the introduction of a
double or triple bond into a hydrocarbon does not have
a dramatic effect on physical properties such as boiling
point. )
27. Structural Isomers
Structures of some hydrocarbons differ only in the
positions of substituent groups or of multiple bonds in
their molecules.
Compounds that have the same molecular formula but
different molecular structures are called isomers.
Isomers have different properties from each other.
butane
2-methylpropane
28. Structural Isomers
Structural isomers are compounds that have the same
molecular formula, but the atoms are joined together n a
different order.
Structural isomers differ in physical properties such as
boiling point and melting point. They also have different
chemical reactivities.
In general, the more highly branched the hydrocarbon
structure, the lower the boiling point of the isomer
compared with less branched isomers.
29. Stereoisomers Isomers
Stereoisomers are molecules in which the atoms are
joined in the same order, but the positions of the atoms
in space are different.
There are two types of steroisomers:
• Geometric isomers
• optical isomers.
30. Geometric Isomers
A double bond between two carbon atoms prevents them
from rotating with respect to each other.
Because of this lack of rotation, groups on either side of
the double bond can have different orientations in
space.
Geometric isomers have atoms joined in the same order,
but differ in the orientation of groups around a double
bond.
31. Geometric Isomers
In the trans configuration, the methyl groups are on
configuration
opposite sides of the double bond.
In the cis configuration, the methyl groups are on the
configuration
same side of the double bond.
Trans-2-butene and cis-2-butene have different physical
and chemical properties.
32. Geometric Isomers
The groups attached to the carbons of the double bond do
not need to be the same.
Geometric isomerism is possible whenever each carbon of
the double bond has at least one substituent.
cis-2-pentene
2-methyl-1-butene
Trans-2-pentene
33. Optical Isomers
Whenever a carbon atom has four different atoms or
groups attached, optical isomers occur.
Asymmetric carbon – a carbon with four different atoms
or groups attached.
The relationship between
the molecules attached to
the carbon is similar to the
relationship between right
and left hands.
34. Optical Isomers
Pairs of molecules that differ only in the way that four
different groups are arranged around a central carbon
atom are called optical isomers.
isomers
The molecules cannot be superimposed because they are
mirror images of each other.
36. Hydrocarbon Rings
In some hydrocarbon compounds, the carbon chain is in
the form of a ring. These are called cyclic
hydrocarbons.
hydrocarbons
Cyclopropane Cyclopentane Cyclohexane
37. Aromatic Hydrocarbons
There is a class of organic compounds that are responsible
for the aroma of spices such as vanilla, cinnamon, cloves
and ginger.
These compounds were originally called aromatic
compounds because they have distinct pleasant odors.
However, not all compounds currently classified as
aromatic have an odor.
Molecules of aromatic compounds contain a single ring or a
group of rings. Benzene (C6H6) is the simplest example of
an aromatic compound.
Aromatic compound is an organic compound that contains
a benzene ring or other ring in which the bonding is like
that of benzene.
38. Aromatic Hydrocarbons
Another name for an aromatic compound is an arene.
arene
Because of the structure of benzene, the properties of
aromatic compounds are quite different from those of
aliphatic compounds.
Benzene is a six-membered carbon ring with a hydrogen
atom attached to each carbon.
One electron from each carbon is free to participate in a
double bond.
39. Benzene Structure
In a benzene molecule, the bonding electrons between
carbon atoms are shared evenly around the ring.
Recall that when two or more equally valid structures can
be drawn for a molecule, resonance occurs.
Benzene and other molecules that exhibit resonance are
more stable than similar molecules that do not exhibit
resonance.
Thus, benzene is not as reactive as six-carbon alkenes.
40. Substituted Aromatic Compounds
Compounds containing substituents attached to a benzene
ring are named as derivatives of benzene.
When the benzene ring is a substituent on an alkane, the
C6H5 group is called a phenyl group.
group
methylbenzene ethylbenzene
3-phenylhexane
41. Disubstituted Benzenes
Some derivatives of benzene have two substituents. These
derivatives are called disubstituted benzenes.
benzenes
There are three structural isomers for the liquid aromatic
compound dimethylbenzene.
Common names for disubstituted benzenes use the terms
ortho, meta, and para in place of numbers.
43. Natural Gas
Much of the world’s energy is supplied by burning fossil
fuels. Fossil fuels are carbon-based because they are
derived from the decay of organisms.
Typically, natural gas is composed of:
• about 80% methane
• 10% ethane
• 4% propane
• 2% butane.
• The remaining 4% consists of nitrogen and
hydrocarbons of higher molar mass.
• also contains a small amount of He)
Methane, the major constituent of natural gas is especially
prized for combustion because it burns with a hot, clean
flame.
44. Combustion of Hydrocarbons
Propane and butane are separated from the other gases in
natural gas by liquefaction and sold in pressurized tank as
liquid petroleum gas (LPG)
Oxygen is necessary for the efficient combustion of a
hydrocarbon. If there is not enough O2 available, the
combustion is incomplete.
Complete combustion gives a blue flame. Incomplete
combustion gives a yellow flame.
Carbon monoxide, a toxic gas, is also formed along with
carbon dioxide and water during incomplete combustion.
45. Petroleum
The organic compounds found in petroleum, or crude oil,
are more complex than those in natural gas.
Most of the hydrocarbons in petroleum are straight-chain
and branched-chain alkanes.
Petroleum also contain small amounts of aromatic
compounds and sulfur, oxygen, and nitrogen containing
organic compounds.
Petroleum is a mixture of hydrocarbons having from one to
40+ carbon atoms. Without further treatment, petroleum is
not very useful.
The mixture must be separated, or refined, into parts called
fractions.
47. Hydrocarbon Cracking
The amounts of products obtained by fractional distillation
are not in proportion to the demand of the market.
Gasoline is the most commonly used product, so other
processes are used to make the supply meet the demand.
Cracking is a controlled process by which hydrocarbons
are broken down or rearranged into smaller, more useful
molecules. (with the aid of a catalyst and with heat)
Example: fractions containing compounds of higher molar
mass are “cracked” to produce the more useful short-
chain components of gasoline and kerosene.
48. Coal Formation - Peat
The first stage in coal formation is an intermediate material
known as peat.
Peat is a soft, brown, spongy, fibrous material with a very
high water content.
When first dug out
peat has a very
high water content.
After it is allowed to
dry, it produces a
low cost but smoky
fuel.
49. Coal Formation - Lignite
If peat is left in the ground, it continues to change.
After a long period of time, peat loses most of its fibrous
texture and becomes lignite, or brown coal.
lignite
Lignite is much harder than peat and has a higher carbon
content (about 50%). The water content is still high.
50. Coal Formation - Bitumious
Continued pressure and heat slowly change lignite into
bitumious, or soft coal.
bitumious
Bitumious coal has a lower water content and higher carbon
content (70 – 80%) than lignite.
51. Coal Formation - Anthracite
In some regions of Earth’s crust, even greater pressures
have been exerted and in those places (eastern PA), soft
coal has been change into anthracite, or hard coal.
anthracite
Anthracite has a carbon content that exceeds 80%, making
it an excellent fuel source.
Coal is classified by its
hardness and carbon
content.
52. Coal Mining
Coal, which is usually found in seams from 1 – 3 meters
thick, is obtained from both underground and surface
mines.
In North America, coal mines are usually less than 100
meters underground.
Much of the coal is so close
to the surface that it is
strip-mined.
Many coal mines in Europe
and other parts of the world
extend 1000 to 1500 meter
below Earth’s surface.
53. Composition of Coal
Coal consists largely of condensed aromatic compounds of
extremely high molar mass.
These compounds have a high proportion of carbon
compared with hydrogen.
Due to the high proportion of aromatic compounds, coal
leaves more soot upon burning than do the more aliphatic
fuels obtained from petroleum.
The majority of the coal that was once burned in North
America contained about 7% sulfur, which burns to form
the major air pollutants SO2 and SO3
54. Composition of Coal
Coal may be distilled to obtain a variety of products: coke,
coal tar, coal gas and ammonia.
Coke is the solid material left after coal distillation. It is used
as a fuel in many industrial processes and is the crucial
reducing agent in the smelting of iron ore.
Because coke is almost pure
carbon, it produces intense heat
And little or no smoke when it
burns.
55. Composition of Coal
Coal gas consists mainly of hydrogen, methane, and carbon
monoxide, all of which are flammable.
Coal tar can be distilled further into benzene, toluene,
napthalene, phenol and pitch.
The ammonia from distilled coal is converted to ammonium
sulfate for use as a fertilizer.
56. Quick Summary
Petroleum and natural gas are derived from marine
organisms. Buried under ocean sediments.
These compounds have a high proportion of carbon
compared with hydrogen.
Due to the high proportion of aromatic compounds, coal
leaves more soot upon burning than do the more aliphatic
fuels obtained from petroleum.
The majority of the coal that was once burned in North
America contained about 7% sulfur, which burns to form
the major air pollutants SO2 and SO3
