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Chapter 25
ORGANIC CHEMISTRY
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25.1 Why Carbon is Different?
25.2 Organic Compounds (groups, functional
groups, naming etc.)
25.3 Representing Organic Molecules
25.4 Isomerism
25.5 Organic Reactions (Omitted)
25.6 Organic Polymers (Biopolymer section
is omitted)
10.1
What is Organic Chemistry?
 Organic chemistry is the field of science that studies the
structure, properties, composition of hydrocarbons (compounds
containing carbon and hydrogen). These compounds may contain
some other elements, including oxygen, nitrogen and halogens.
Glucose molecule
Fat molecule
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10.1
Why Carbon is Different
All known INORGANIC compounds ~100,000
ORGANIC compounds, MILLIONS
 Electron configuration: [He]2s22p2
shows that C atom effectively prohibits
ion formation and tends to share
electrons.
 Carbon atom has a small atomic radius
which gives rise to short and strong
carbon bonds and, hence, stable
compounds. (14Si?? in the same group..)
 C atoms can form σ and strong π bonds.
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These attributes enable carbon to form chains (straight,
branched, and cyclic) containing single, double, and triple
carbon-carbon bonds. Carbon’s formation of chains is called
catenation.
Aromatic Compounds
Organic compounds that are related to benzene, or that contain
one or more benzene rings, are called aromatic compounds.
Aliphatic Compounds
Organic molecules that do not contain the benzene ring are
called aliphatic compounds.
10.2
Alkanes
 Alkanes are simple organic compounds that consist of only
carbon and hydrogen. They contain only single bonds.
CH4
Methane
C2H6
Ethane
C3H8
Propane
C4H10
Butane
C5H12
Pentane
General Formula
CnH2n+2
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10.2
Alkanes
C6H14
Hexane
C7H16
Heptane
C8H18
Octane
C9H20
Nonane
C10H22
Decane
General Formula
CnH2n+2
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10.2
Alkyl Groups
 An alkyl group (R) is a portion of a molecule that resembles
an alkane. An alkyl group is formed by removing one
hydrogen atom from the corresponding alkane.
 Alkyl groups are represented in organic compounds with R.
Methyl
Ethyl
Propyl
Isopropyl
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10.2
Alkyl Groups
Butyl
tert-Butyl
Pentyl
Isopentyl
Hexyl
Heptyl
Octyl
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Substituents/groups
F – Fluoro
Cl – Chloro
Br – Bromo
I - Iodo
Functional Groups
 A functional group is a
group of atoms that
determines many of the
molecule’s properties, and
that are responsible for
chemical reactions.
 Some commonly
important functional
groups:
o Alcohol
o Carboxylic acid
o Aldehydes
o Esters
o Ketone
o Amines
o Amides
10.2
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10.2
Functional Groups
Alcohol
Carboxylic acid
Ester
Aldehyde
Ketone
R represents an alkyl group.
R’ represents a second alkyl group that may or may not be identical to
the first alkyl group R.
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10.2
Functional Groups
Amine
Amine
Amine
Amide
Amide
Amide
1, 2 and 3 indicate one, two, and three R groups bonded to
the N atom, respectively
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10.2
Identifying Functional Groups
R-CO-H
Aldehyde
R-OH
Alcohol
R-NH2
1 amine
R-COOH
Carboxylic
acid
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10.2
Identifying Functional Groups
R-COOH
Carboxylic
Acid
R-CO-R’
Ketone
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10.2
Identifying Functional Groups
NH2
O
C
CH3
O
O
C
OH
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Identifying Functional Groups
Naming Organic Compounds
Molecular formula is not enough as the properties of organic
compounds vary significantly depending on the group and
functional group position..
Hexane (C6H14)
10.2
Naming Organic Compounds
 Organic compounds are named using the “International Union
of Pure and Applied Chemistry” (IUPAC) rules.
 There are:
o Systematic names: names that are based on IUPAC system.
o Trivial names: names that are commonly used but are not
based on IUPAC system.
F
F
Systematic Name
Trivial Name
Trichloromethane
Chloroform
Dichlorodifluoromethane
Freon
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Naming Organic Compounds
(Nomenclature)
10.2
 How to name alkanes.
methyl
1. Identify the longest
at position 3
H
continuous carbon chain to
get the parent name.
hexane
H C H
2. Number the carbons in the
H H
H H H
continuous chain, beginning
H C1 C2 C3 C 4 C 5 C 6 H
at the end closest to the
substituent.
H H H H H H
3. Identify the substituent and
use a number and a prefix to
3-Methylhexane
specify location and identity,
respectively.
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10.2
Naming Organic Compounds
 How to name alkanes.
4. When two or more
substituents are there:
o If they are identical, use
prefixes (di, tri, tetra, …)
to indicates the number
of substituents.
o Also, use numbers as
usual to indicate which C
atom they are bonded
to.
H
methyl
H C H
H H
H H H
H C1 C2 C3 C4 C5 C6 H
H H
H H H
H C H
methyl
H
3,3-Dimethylhexane
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10.2
If the carbon number is same in 2 chains, choose the chain with more
substituents
 How to name alkanes.
4. When two or more substituents
are there:
H
H C H
H
methyl
H H H H
If the substituents are not
H C1 C2 C3 C 4 C 5 C 6 H
identical, follow the same
H H
H H H
procedure for identical
H C H
substituents. However, the
substituent names must be put in
H C H ethyl
an alphabetical order. (prefixes are
H
not used to determine the
3-Ethyl-2-methylhexane
alphabetization)
Notice that incorrect numbering would lead to the name 3-isopropylhexane.
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10.2
Naming Organic Compounds
 Exercise:
Name the following organic compounds:
H
H
H
H Cl
C
H
H
H
H
H C
C
C
C
C
H
H
H
H
H
H
2-Chloro-3-methylpentane
C
H
H
H
C
C
C
H
H
H
H
H
H
C
C
C
H
H
C
H
C
H
H
C
H
H
H
H H
H
3-Ethyl-3-methylheptane
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Naming Organic Compounds Containing
Functional Groups
 How to name alcohols.
1. Identify the longest chain
H
that includes the –OH
group.
2. Do numbering such that the
C bearing –OH group is
given the lowest number.
3. Change the –e ending to -ol.
4. If the chain also contains an
alkyl substituent, give the
–OH group the lowest
number.
10.2
H H H O H
C4 C3 C 2 C1 H
alcohol
H H H H
1-Butanol
Butane
H
H
H
H
O
H
C
C
C
C
H
H
H
H
H C
H
H
3-Methyl-1-butanol
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What we discussed in last lecture
Organic chemistry
How C is different
Aromatic & aliphatic compounds
Alkane
Alkyl groups & substituents
Functional groups
Naming organic compounds
Today…
Organic Compounds (groups, functional
groups, naming etc.)
Representing Organic Molecules
Isomerism
10.2
Containing Carboxy Groups
H H H O
 How to name carboxylic acids.
1. Identify the longest chain
H C4 C3 C2 C1 O H
that includes the carboxy
H H H
Carboxylic
group.
acid
Butanoic acid
2. Do numbering starting with
the carbonyl (C=O) carbon.
H F H O H
3. Change the – e ending to –
H C C C C O
1
2
oic acid.
3
H
H
4. Use numbers and prefixes to
H C4 H
indicate the position and
H C H
identity of any substituents.
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H
3-Fluoro-3-methyl-pentanoic acid
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Naming Organic Compounds
Containing Functional Groups
10.2
What is the name of the carboxylic acids shown below?
Br
Ethanoic acid
Acetic acid
Bromoethanoic acid
Trivial name
Bromoacetic acid
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10.2
Naming Organic Compounds
Containing Functional Groups
 How to name esters.
Esters are named as
derivatives of carboxylic
acids by:
o locating the ester group.
o locating the main carbon
chain which is the R
group connected to the
C=O group.
o locating the substituent.
o replacing the –ic acid
ending with – oate.
Ester
group
H H H O
H
H C C3 C2 C1 O C H
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H H H
H
Methyl butanoate
H H H
O H
Ester
group
H C C C O C C H
Trivial name
H H H
H
Propyl ethanoate
Propyl acetate
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10.2
Naming Organic Compounds
Containing Functional Groups Aldehyde
 How to name aldehydes.
1. Identify the longest chain
that includes the carbonyl
group.
2. Change the –e ending to - al.
3. Number starting with the
carbonyl (C=O) carbon.
4. Use numbers and prefixes to
indicate the position and
identity of any substituents.
H H O
H C3 C2 C1 H
H H
Propanal
H
O
Cl H
H
C
C
C
C
H
H
1
2
H
C3 H
H
C4 C5
H
H
Cl
H H
2,5-Dichloro-2-ethylpentanal
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10.2
Naming Organic Compounds
Containing Functional Groups
H H O H
 How to name ketones.
1. Identify the longest chain that
includes the carbonyl group.
2. Number to give the carbonyl
group (C=O) the lowest possible
number.
3. Change the –e ending to - one.
4. Use numbers and prefixes to
indicate the position and
identity of any substituents.
Carbonyl
H C 4 C3 C 2 C1 H
H H
H
2-Butanone
O
H
H
H
I
C
C
C
C
C
H
H
H
H
4
H
H
C
3
5
6
7
8
H
H
H
H
C
C2 C1
H
H
H
H
8-Iodo-2-methyl-4-octanone
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10.2
Naming Organic Compounds
Containing Functional Groups
Amine
 How to name primary amines.
1. Identify the longest chain that
includes the –NH2 group.
2. Number C atoms so that the C
atom to which the –NH2 group
is bonded is given the lowest
possible number.
3. Change the –e ending to amine.
4. Use numbers and prefixes to
indicate the position and
identity of any substituents.
H H H
H C C N H
2
1
H H
Ethanamine
H H H H H H
H C5 C4 C 3 C2 C 1 N H
H H H H H
1-Pentanamine
H H H H H
Cl
C C C3 C2 C Cl
5
4
1
H
Cl H H N
H
1,5,5-Trichloro-2-pentanamine H
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10.2
Naming Organic Compounds
Containing Functional Groups
Amide
 How to name primary amides.
Primary amides can be named
as derivatives of carboxylic
acids by replacing the –ic acid
ending with – amide.
H H O
H C C2 C N H
3
1
H H
H
Propanamide
H H F H H O
H C C C C C C N H
6
5
H
4
3
2
H H H
1
H
H C H
H
4-Fluoro-5-methylhexanamide
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10.2
Naming Organic Compounds
 Exercise:
4
1
2
3
5
7
6
8
5
6
3
7
2
8
1
9
10
4-ethyl-7-methyl-5-propyldecane
4
4-ethyl-5-propyloctane
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Representing Organic Molecules
Condensed Structural Formulas
Kekulé Structures
Skeletal Structures
Resonance
Representing Organic Molecules
Condensed Structural Formulas
A condensed structural formula, or simply a condensed
structure, shows the same information as a structural formula,
but in a condensed form.
Representing Organic Molecules
Condensed Structural Formulas
Representing Organic Molecules
10.3
Kekulé structure
 Kekulé structure: It is similar to Lewis structure but without
showing the lone pairs. It is very commonly used in organic
chemistry.
Kekulé structure
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Representing Organic Molecules
Kekulé structure
Representing Organic Molecules
Skeletal structure
When a heteroatom is present?
Skeletal structure
10.3
Representing Organic Molecules
 Exercise:
Write a molecular formula and condensed structural formula for
the following:
C4H8
C2H5NO
Molecular formula
Molecular formula
CH3(CH)2CH3
CH3CONH2
Cond. Structural formula
Cond. Structural formula
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10.3
Representing Organic Molecules
 Exercise:
Write the molecular formula and a structural formula for the
following molecule.
O
CH3COCH2CH3
Structural formula
C4H8O
Molecular formula
What is the correct name of this compound?
2-butanone
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10.3
Resonance
 Resonance is repositioning of electrons to produce other
equivalent structures of the molecule.
o You will need to review how to draw Lewis structures for
simple organic compounds.
 Example: Draw the Lewis structure of nitrate ion (NO3‒) and
show resonance structure.
1–
O
N
O
O
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10.3
Resonance
 The nitrate ion structure is the
average of all the three equivalent
structures, not one of them.
 The three NO bonds are found
from experiments to be identical.
Resonance structures:
1–
O
N
O
O
1–
O
O
N
O
1–
O
N
O
O
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10.3
More Examples on Resonance
Structures
 The anion produced from ethanoic acid (ethanoate).
 Benzene molecule (C6H6)
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Why acetic acid loses protons much
more easily than alcohol??
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ISOMERISM
• Isomers are molecules that have the same molecular
formula, but have a different arrangement of the atoms in
space.
• Excludes any different arrangements which are simply due
to the molecule rotating as a whole, or rotating about
particular bonds.
25.4
ISOMERISM
Constitutional or Structural Isomerism
Stereoisomerism
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25.4
ISOMERISM
Constitutional Isomerism
Constitutional isomerism occurs when the same atoms can be
connected in two or more different ways.
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25.4
ISOMERISM
Constitutional Isomerism
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How many structural isomers hexane (C6H14) has,
draw the structure?
ISOMERISM
Stereoisomerism
Stereoisomers are those that contain identical bonds but differ
in the orientation of those bonds in space.
Two types of stereoisomers exist: geometrical isomers and
optical isomers.
Geometrical isomers occur in compounds that have restricted
rotation around a bond.
Stereoisomers that are mirror images of each other, but are not
superimposable, are called optical isomers.
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25.4
ISOMERISM
Stereoisomerism (Geometrical Isomerism)
Geometrical isomer
Geometrical isomer
Structural isomer
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25.4
ISOMERISM
Stereoisomerism (Optical Isomerism)
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25.4
ISOMERISM
Stereoisomerism (Optical Isomerism)
Molecules with nonsuperimposable mirror images are called
chiral; and a pair of such mirror-image molecules are called
enantiomers.
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25.4
ISOMERISM
Representing three-dimensional objects on two-dimensional surface
it often is necessary to represent tetrahedral molecules (threedimensional objects) on paper (a two-dimensional surface).
This is done using dashes
to represent bonds that
point behind the page,
and wedges to represent
bonds that point in front
of the page.
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25.4
ISOMERISM
Determination of chirality or enantiomers
One property of chiral molecules is that the two enantiomers
rotate the plane of plane-polarized light in opposite directions;
that is, they are optically active.
If the plane of polarization is rotated to the right, the isomer is
said to be dextrorotatory and is labeled d; if it is rotated to the
left, the isomer is called levorotatory and labeled l.
Enantiomers always rotate the light by the same amount, but
in opposite directions. Thus, in an equimolar mixture of both
enantiomers, called a racemic mixture, the net rotation is zero.
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25.4
Isomerism
Stereoisomerism
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POLYMER
Addition Polymers
Condensation Polymers
25.6
Organic Polymers
Addition Polymers
Polymers are molecular compounds, either natural or
synthetic, that are made up of many repeating units called
monomers.
Addition polymers form when monomers such as ethylene
join end to end to make polyethylene.
Reactions of this type can be initiated by a radical—a species
that contains an unpaired electron.
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25.6
Organic Polymers
Addition Polymers
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25.6
Organic Polymers
Addition Polymers
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25.6
Organic Polymers
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25.6
Organic Polymers
Condensation Polymers
Reactions in which two or more molecules become connected
with the elimination of a small molecule, often water, are
called condensation reactions.
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25.6
Organic Polymers
Condensation Polymers
Condensation polymers form when molecules combine
through functional groups with the elimination of a small
molecule, often water.
Many condensation polymers are copolymers, meaning that
they are made up of two or more different monomers.
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25.6
Organic Polymers
Condensation Polymers
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Exercise
Draw the structure of polypropylene, showing atleast 2 repeating
units.
Draw the structure of monomer used to make the below polymer.
Polymethyl methacrylate
Draw the structure of monomer used to make the below polymer.
n
Draw the structure of monomer used to make the below polymer.
Answers
monomer
n
monomer
Answers
monomer
monomer
polymer