Introduction to Organic Chemistry
Organic chemistry is the study of compounds that
contain the element carbon.
• Organic chemicals affect virtually every facet of
our lives.
• Products such as clothes, foods, medicines,
gasoline, refrigerants, and soaps are composed
almost solely of organic compounds.
• Because organic compounds are composed of
covalent bonds, their properties differ a great
deal from those of ionic inorganic compounds.
1
Characteristic Features of Organic
Compounds
1. All organic compounds contain carbon atoms and
most contain hydrogen atoms.
• Carbon has four valence electrons available for
bonding.
• Hydrogen has a single valence electron and can
only form single bonds.
2
Characteristic Features of Organic
Compounds
2. Carbon forms single, double, and triple bonds to
other carbon atoms.
3
Characteristic Features of Organic
Compounds
3. Some compounds have chains of atoms and some
compounds have rings.
4
Characteristic Features of Organic
Compounds
4. Organic compounds may also contain elements
other than carbon and hydrogen.
• Any atom that is not carbon or hydrogen is called
a heteroatom.
• Each heteroatom forms a characteristic number of
bonds, determined by its location in the periodic
table.
• The common heteroatoms (N, O, F, Cl, Br, and I)
also have nonbonding, lone pairs of e−, so that
each atom is surrounded by eight electrons.
# of bonds
+
# of lone pairs
=
4
5
Characteristic Features of Organic
Compounds
4. Organic compounds may also contain elements
other than carbon and hydrogen, (heteroatoms )
Each heteroatom forms a characteristic number of
bonds, determined by its location in the periodic
table.
6
Characteristic Features of Organic
Compounds
The most common multiple bond between carbon
and a heteroatom is a carbon–oxygen double bond.
7
Drawing Organic Molecules
Condensed Structures
In a condensed structure, all of the atoms are drawn in,
but the two-electron bond lines and lone pairs on
heteroatoms are generally omitted.
• A carbon bonded to 3 Hs becomes CH3.
• A carbon bonded to 2 Hs becomes CH2.
8
Drawing Organic Molecules
Condensed Structures
• Sometimes structures are further simplified by
using parentheses around like groups.
• Two CH2 groups bonded together become
(CH2)2.
• Two CH3 groups bonded to the same carbon
become (CH3)2C.
9
Drawing Organic Molecules
Skeletal Structures
When drawing a skeletal structure:
• Assume there is a carbon atom at the junction of
any two lines or at the end of any line.
• Assume there are enough hydrogens around each
carbon to give it four bonds.
• Draw in all heteroatoms and the hydrogens directly
bonded to them.
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Drawing Organic Molecules
Skeletal Structures
11
Functional Groups
• A functional group is an atom or group of atoms
with characteristic chemical and physical
properties.
• A functional group contains a heteroatom, a
multiple bond, or sometimes both.
• The letter R is used to abbreviate the carbon
and hydrogen portion of a molecule.
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Functional Groups
Hydrocarbons
Hydrocarbons are compounds that contain only
carbon and hydrogen.
• Alkanes have only C–C single bonds and no
functional group.
• Alkenes have a C–C double bond as their
functional group.
• Alkynes have a C–C triple bond as their functional
group.
• Aromatic hydrocarbons contain a benzene ring,
a six-membered ring with three double bonds.
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Functional Groups
Compounds Containing a C=O group
• Carbonyl groups (carbon–oxygen double bonds)
are present in several different compounds.
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Functional groups
.
CH3
CH3
Alcohols
CH3
CH2 OH
Aldehydes
O
CH3
C H
Esters
Alkynes
Alkenes
Alkanes
CH2
CH2
Ethers
CH3
O CH3
Ketone
O
CH3
C CH3
Amines
CH CH
Thiols
CH3
CH2
Organic acids
O
CH3
C O H
Amides
O
O
CH3
C O CH3
SH
CH3
NH2
CH3
C NH2
Alkanes
Introduction
Alkanes are hydrocarbons having only C–C and
C–H single bonds.
• Alkanes that contain chains of C atoms but
no rings are acyclic alkanes and have the
general formula CnH2n+2.
• Acyclic alkanes are called saturated alkanes
because they have the maximum number of H
atoms per C atom.
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Alkanes
Introduction
• Cycloalkanes contain C atoms joined in one
or more rings.
• They have the general formula CnH2n.
All alkane molecules have names that end in the
suffix “-ane.”
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Simple Alkanes
Acyclic Alkanes Having
Fewer than Five Carbons
• Methane is a one-carbon alkane.
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Simple Alkanes
Acyclic Alkanes Having
Fewer than Five Carbons
• Ethane is a two-carbon alkane.
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Simple Alkanes
Acyclic Alkanes Having
Fewer than Five Carbons
• Propane is a three-carbon alkane.
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Simple Alkanes
Acyclic Alkanes Having
Fewer than Five Carbons
• The following two representations of propane are
equivalent:
• The bends in a carbon chain don’t matter when it
comes to identifying different compounds.
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Simple Alkanes
Acyclic Alkanes Having
Fewer than Five Carbons
• Butane has four-carbon atoms in a row. It is a
straight-chain alkane.
• Isobutane has three carbon atoms in a row and one
bonded to the middle. It is a branched-chain alkane.
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Simple Alkanes
Acyclic Alkanes Having
Fewer than Five Carbons
• Butane and isobutane are isomers of each other.
• Isomers are two different compounds with the
same molecular formula.
• Constitutional isomers differ in the way the atoms
are connected to each other.
• Another example of constitutional isomers:
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Simple Alkanes
Acyclic Alkanes Having Five or More Carbons
• As the number of C atoms increases, the number
of possible isomers increases.
• Pentane is a five-carbon alkane with three isomers:
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Simple Alkanes
Acyclic Alkanes Having Five or More Carbons
• After pentane, the following names apply:
# of C’s
Name
6
hexane
CH3CH2CH2CH2CH2CH3
7
heptane
CH3CH2CH2CH2CH2CH2CH3
8
octane
CH3CH2CH2CH2CH2CH2CH2CH3
9
nonane
CH3CH2CH2CH2CH2CH2CH2CH2CH3
10
decane
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
Structure
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An Introduction to Nomenclature
The IUPAC System of Nomenclature
• IUPAC stands for International Union of Pure and
Applied Chemistry.
• The IUPAC system of nomenclature provides a
system of naming organic compounds.
• Using the IUPAC system, each organic compound
gets an unambiguous name.
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Alkane Nomenclature
Naming Substituents
• Carbon substituents are called alkyl groups.
• An alkyl group is formed by removing 1 H from an
alkane.
• To name an alkyl group, change the “-ane” ending
of the parent alkane to “-yl.”
• Each alkyl group has a bond that can then be
attached to something else.
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Alkane Nomenclature
Naming Substituents
28
Alkane Nomenclature
Naming Substituents
29
Alkane Nomenclature
Naming an Acyclic Alkane
HOW TO Name an Alkane Using the IUPAC System
• The longest chain may not be written horizontally.
• It does not matter if the chain is straight or has
bends.
• All three examples below have 6 Cs in their
longest chain:
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Alkane Nomenclature
Naming an Acyclic Alkane
HOW TO Name an Alkane Using the IUPAC System
Step [1]
Find the parent carbon chain and add the
suffix.
• Find the longest continuous carbon chain, and
name it with an “-ane” ending.
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Alkane Nomenclature
Naming an Acyclic Alkane
HOW TO Name an Alkane Using the IUPAC System
Step [2]
Number the atoms in the carbon chain to
give the first substituent the lower number.
CORRECT
INCORRECT
32
Alkane Nomenclature
Naming an Acyclic Alkane
HOW TO Name an Alkane Using the IUPAC System
• The following compound contains two methyl
groups, so we use the name dimethyl for them.
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Alkane Nomenclature
Naming an Acyclic Alkane
Sample Problem 10.9
Give the IUPAC name for the following compound.
methyl at
C2
CH3
ethyl at C5
CH3CH2 H
CH3 C
CH2CH2 C
H
H
C
CH2CH3
CH3
1 2
5
6
longest chain is 8 Cs = octane
methyl at C6
5-ethyl-2,6-dimethyloctane
Answer
34
Cycloalkanes
Naming Cycloalkanes
35
Cycloalkanes
Naming Cycloalkanes
HOW TO Name a Cycloalkane Using the IUPAC System
Step [1]
Find the parent cycloalkane.
36
Cycloalkanes
Naming Cycloalkanes
HOW TO Name a Cycloalkane Using the IUPAC System
Step [2]
Name and number the substituents.
• No number is needed for a cycloalkane with a
single substituent.
37
Cycloalkanes
Naming Cycloalkanes
HOW TO Name a Cycloalkane Using the IUPAC System
For rings with two or more substituents:
• begin numbering at one substituent
• then, proceed around the ring to give the second
substituent the lower number
For two different substituents, number the ring to
assign the lower number to the substituents
alphabetically.
38
Cycloalkanes
Naming Cycloalkanes
HOW TO Name a Cycloalkane Using the IUPAC System
Earlier letter = lower number
ethyl group at C1
methyl group at C3
1-ethyl-3-methylcyclohexane
(not 3-ethyl-1-methylcyclohexane)
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Physical Properties
• Alkanes contain only nonpolar C–C and C–H
bonds.
• Alkanes exhibit only weak intermolecular forces,
so they have low melting points and boiling points.
• Smaller alkanes are gases at room temperature,
whereas larger alkanes are liquids.
• Alkanes are insoluble in water.
• Alkanes are less dense than water, meaning that
they will float on the surface of water.
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Physical Properties
• As the number of carbons in an alkane increases,
the boiling point increases:
41
Combustion
• Alkanes have no functional group, so they undergo
few reactions.
• Combustion is the only reaction of alkanes in this
chapter. It is an oxidation reaction.
• In the combustion reaction, alkanes burn in the
presence of O2 gas to form CO2 and H2O.
42
Combustion
• The products, CO2 + H2O, are the same, regardless
of the identity of the alkane that undergoes
combustion.
• Combustion of alkanes in the form of natural gas,
gasoline, or heating oil releases energy for heating
homes, powering vehicles, and cooking food.
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Combustion
• If there is not enough O2 to react, incomplete
combustion may occur, and carbon monoxide (CO)
is formed instead of carbon dioxide (CO2).
• Carbon monoxide is a poisonous gas that binds
to hemoglobin in blood, thereby reducing the
amount of O2 that can be transported to cells.
44