Introduction To Organic
Chemistry
Lecture 1
12.1 Introduction
Learning Outcomes:
At the end of the lesson the students should be able to :
1.
List the elements that made up organic compounds C, H,
O, N, P, S and halogens.
2.
State the ability of carbon to form 4 covalent bonds with
other carbons or elements.
3.
Differentiate between saturated and unsaturated organic
compounds.
4.
Give examples of organic compounds used in medicine,
engineering, biotechnology and agriculture.
WHAT IS ORGANIC CHEMISTRY?
Organic chemistry is the chemistry of carbon
compounds.
Organic compounds contain H as well as C, while
other common elements are O, N, the halogens, S and
P.
There are many varieties of organic compounds
( more than 10 millions!!!)
They may exist as simple or complex molecules; as
gases, liquids or solid and coloured or colourless.
Examples :CH4
methane (a component of natural gas)
OCOCH3
COOH
methyl salicylic acid (aspirin-a drug)
O
CH2
C
S
NH
O
N
COOH
penicillin (an antibiotic)
Cl
CH
Cl
CCl3
dichlorodiphenyltrichloroetane
(DDT- a pesticide component)
All organic compounds consist of carbon atom.
Properties of carbon atom:
-has 4 valence electrons.
-can form 4 covalent bonds.
C C
Single bond
C
C
Double bond
C
C
Triple bond
Hydrocarbons
saturated
Contains only single
bonds ( -C-C- )
Examples: alkanes,
cycloalkanes
unsaturated
Contains at least one
carbon-carbon double
bond (-C=C-) or triple
bond (-C C-).
Examples: alkenes,
alkynes.
Uses of organic compounds
Medicine
Engineering
Biotechnology
Agriculture
Antibiotics are used to
fight bacterial and fungal
infections
Gasoline-as a fuel for
internal combustion
engines.
Genetic information like
DNA
DDT-as insectisides to kill
harmful insects.
Lecture 2:
12.2 Molecular and Structural Formulae
Learning Outcomes:
At the end of the lesson the students should
be able to :
Define structural formula.
Draw structural formula in the form of expanded,
condensed and skeletal structures based on the
molecular formula.
Explain primary (1°), secondary (2°), tertiary (3°)
and quaternary (4°) carbon.
Structural formula shows how the
atoms in a molecule are bonded to
each other.
3 types of structural formula:
• condensed structure
• expanded structure
• skeletal structure
2- Dimensional formula
Condensed Structure
Does not show single bonds between carbon
and hydrogen atoms, but double and triple bonds
are shown.
All atoms that are attached to a carbon are
written immediately after that carbon.
C4H9Cl
CH3CHCH2CH3
(Condensed structure)
Examples:
ii) Cyclohexane, C6H12
H2C
H2
C
CH2
H2C
C
H2
CH2
iii) Aldehyde, CH3CHO
O
CH3CH
Expanded Structure
Expanded structures indicate how atoms are
attached to each other but are not representations
of the actual shapes of the molecules.
C4H9Cl
Molecular
Formula
H
H
H
H H
C
C
C
C
H
Cl
H
H
H
Expanded structure
Examples:
i) Alcohol (C2H6O)
H
H
H
C
C
H
H
OH
ii) Carboxylic acid (C3H6O2 )
H
H
H
O
C
C
C
H
H
OH
Skeletal Structure
Shows only the carbon skeleton.
Hydrogen atoms are not written.
Other atoms such as O, Cl, N etc. are shown.
i)
CH3CH(Cl)CH2CH3
=
Cl
ii)
H2C
CH2
H2C
CH2
=
3- Dimensional formula
( wedge – dashed wedge – line formula )
Describes how the atoms of a molecule
are arranged in space.
Example : Bromoethane
Br
H
H
C
H
H
Br
H
H
C
C
C
H
H
or
H
H
Br
or
H
Indication ::bonds that lie in the plane
:bonds that lie behind the plane
:bonds that project out of the plane
Br
H
Classification of C atoms:
A carbon atom can be classified as
primary carbon(1o) →bonded to 1 C
secondary carbon(2o) → bonded to 2 C
tertiary carbon(3o) → bonded to 3 C
quarternary carbon(4o) → bonded to 4 C
H
H
C
H
CH3
10 carbon
10 carbon
CH3
H
C
CH3
30 carbon
CH3
1
H H CH3
1
CH3
1
1
H C C C CH2 C CH3
H H H
CH3
1
H H CH3
CH3
2
H C C C CH2 C CH3
2
H H H
CH3
H H CH3
3
CH3
4
H C C C CH2 C CH3
H H H
CH3
Question
Expanded
Structure
Condensed
Structure
Skeletal
Structure
CH3(CH2)CCl(CH3)2
O
H
H H
CH3
C C CH
H H
CH3
12.3 FUNCTIONAL GROUPS
AND HOMOLOGOUS SERIES
Lecture 3
Functional Group and Homologous Series
Learning Outcomes:
At the end of the lesson the students should be able
to :
• Define functional group.
• Name functional groups and classify organic
compounds according to their functional groups.
• Define homologous series and explain general
characteristics of its members.
Functional group
is an atom or group of atoms in an organic
molecule which characterised the molecule
and enables it to react in specific ways
which determines its chemical properties.
Functional groups are important for three
reasons:
i.
ii.
iii.
A basic by which organic compounds are
divided into different classes.
A basic for naming organic compounds
A particular functional group will always
undergo similar types of chemical
reactions.
Homologous Series
is series of compounds where each member
differs from the next member by a constant
– CH2 unit
Members of the same homologous series
are called homologs.
Homologs Features
1.
Obey a general formula:
Examples:
•
Alkane: CnH2n+2
•
Alkene: CnH2n
•
Alcohol : CnH2n+1OH
2.
3.
Differ from the successive homolog by a CH2
unit
Show a gradual change in the physical properties
4.
5.
6.
Have same functional group
Have similar chemical properties
Can be prepared by similar general methods
Classification of organic compound
Class of
Compound
Functional Group
Example
Structure
Alkane
Alkene
Alkyne
Name
CH3-CH3
-C=C-
carbon-carbon
double bond
CH3CH=CH2
-C C-
carbon-carbon
triple bond
CH3C CCH3
Aromatic
Haloalkane
Benzene ring
X (F, Cl, Br, I) Halogen
Alcohol
-OH
Hydroxyl
Phenol
-OH
Hydroxyl
-C-O-C-
Alkoxide
Ether
-CH3
CH3Cl
CH3-OH
-OH
CH3-O-CH3
Aldehyde
-C=O
H
Ketone
R-C=O
R
Carboxylic
acid
-C=O
OH
Ester
-C-O-CO
Acyl chloride
-C=O
Cl
Carbonyl
CH3-C=O
H
Carbonyl
CH3-C=O
CH3
Carboxyl
CH3-C=O
OH
Carboalkoxy
CH3-C=O
OCH3
CH3-C=O
Cl
Anhydride
O O
-C-O-C-
Amide
-C=O
N-
Amine
-NH2
Nitrile
-C N
O O
CH3C-O-CCH3
Carboxamide CH3-C=O
NH2
Amino
Cyano group
CH3-NH2
CH3C
N
Exercises:
1. Identify the functional group in the following
molecules
a)(CH3)3CCH2CH=CH2
b)(CH3)3CCH=CHCH2-OH
c)
O
O
C
OH C O C
CH3 CH2 OH CH2
CH3
C
C
O
C
NH2 CH C
CH2 O
CH3
O
CH
C
O
CH3
NH2
12.4 Isomerism
Learning Outcomes:
At the end of the lesson the students should be
able to :
Define isomerism.
Explain constitutional isomerism.
chain isomers
positional isomers
functional group isomer
Isomerism
Structural/
Constitutional Isomerism
Chain
Isomerism
Positional
Isomerism
Stereoisomerism
Functional Group
Isomerism
diastreomer enantiomer
cis-trans
isomerism
other
diastereomers
Isomerism
is the existence of different compounds with
the same molecular formula but different
structural formulae.
Different structural formula that have the same
molecular formula are called isomers.
1) Constitutional isomers (Structural isomers)
• are isomers with the same molecular formula
but differ in the order of attachment of atoms.
2) Stereoisomers
• are isomers with the same molecular formula
but different arrangement of atoms in space
Constitutional isomerism
Isomerism resulting from different order of
attachment of atoms.
Three types
a) Chain/skeletal isomerism
b) Positional isomerism
c) Functional group isomerism
•
a) Chain/skeletal isomerism
The isomers differ in the carbon skeleton
(different carbon chain).
They possess the same functional group and
belong to the same homologous series.
Example:
C5H12
CH3CH2CH2CH2CH3
CH3
CH3CHCH2CH3
CH3
CH3CCH3
CH3
2)Positional isomerism
These isomers have a substituent group/ functional
group in different positions.
Examples
•
C3H7Cl
CH3CH2CH2Cl
1-chloropropane
CH3CHCH3
Cl
2-chloropropane
C4H8
CH2=CHCH2CH3
CH3CH=CHCH3
1-butene
2-butene
C8H10
CH3
CH3
CH3
CH3
CH3
1,2-dimethylbenzene
1,3-dimethylbenzene
CH3
1,4-dimethylbenzene
C6H13N
NH2
CH3
CH3
H2N
CH3
CH2NH2
NH2
3)Functional group isomerism
These isomers have different functional groups and
belong to different homologous series with the same
general formula.
Different classes of compounds that exhibit
functional group isomerism :General formula
Classes of compounds
CnH2n+2O ; n > 1
alcohol and ether
CnH2nO ; n ≥ 3
aldehyde and ketone
CnH2nO2 ; n ≥ 2
carboxylic acid and ester
CnH2n ; n ≥ 3
alkene and cycloalkane
Examples
CH3CH2OH
C2H6O
ethanol
C3H6O
CH3CCH3
O
propanone
C3H6O2
CH3CH2COH
O
propanoic acid
CH3OCH3
dimethyl ether
CH3CH2CH
O
propanal
CH3COCH3
O
methyl ethanoate
Exercise:
1. State how many are isomers with the following molecular
formulae, identify the type of isomerism and draw the
structural formula of the isomers.
a) C5H10
b) C5H10O2
c) CH3CH=C(Cl)CH3
d) C4H6Cl2
e) CH3CH2CH(OH)CH(Br)CH2CH3
Lecture 5
12.4 Isomerism
Learning Outcomes:
At the end of the lesson the students should
be able to :
• Define stereoisomerism.
• Describe cis-trans isomerism due to
restricted rotation about C=C bond and CC
bond in cyclic compounds
• Identify cis-trans isomerism of a given
structural formula.
Stereoisomerism / optical isomerism :
Isomerism that resulting from different
spatial arrangement of atoms
in molecules.
Two subdivisions of stereoisomers:
i)
Enantiomers (mirror image)
ii) Diastereomers (non-mirror image)
Diastereomer
Cis-Trans Isomerism
 The requirements for geometric isomerism
:
i) restricted rotation about a C=C,double
bond in alkenes, or a C-C single bond
in cyclic compounds.
ii) each carbon atom of a site of restricted
rotation has two different groups
attached to it.
Examples
H
CH3
C
C
H3C
H
H
C
H
H
cis-2-butene
CH3 H
H
CH3 CH3
CH3
C
trans-2-butene
H
H3C
CH3
cis-1,2-dimethylcyclohexane
trans-1,2-dimethylcyclohexane
If one of the doubly bonded carbons has 2 identical
groups, geometric isomerism is not possible.
Example
H3C
CH3
C
H3C
C
H
No cis – trans isomer
Lecture 6
12.4
Isomerism
Learning Outcomes:
•
•
•
•
•
•
•
At the end of the lesson the students should be able to
:
Identify cis-trans isomerism of a given structural
formula.
Define chirality centre and enantiomers.
Identify chirality centre in a molecule.
Explain optical activity of a compound.
Draw a pair of enantiomers using 3-dimensional
formula.
Define racemate.
State the applications of chiral compounds in daily
life.
Enantiomer
Optical Isomerism
•
Optically active compounds have the ability to
rotate plane-polarized light to the right
(dextrorotary) and to the left (levorotary)
•
The angle of rotation can be measured with an
instrument called polarimeter.
Polarimeter
The requirements for optical isomerism :i)
molecule contains a chiral carbon or chirality centre
or stereogenic centre (a sp3-hybridized carbon atom
with 4 different groups attached to it)
P
Q
C*
S
PQRS
*designates chiral centre
R
ii) molecule is not superimposable with its mirror
image.

Enantiomers
a pair of mirror-image that are not superimposable.
Example:i) 2-butanol ,
CH3CHCH2CH3
OH
H3C
CH2CH3
CH2CH3
C*
C
H
OH
H
enantiomers
CH3
OH
ii) 2-hydroxypropanoic acid,
COOH
H
OH
CH3
enantiomers
COOH
HO
H
CH3
12.4.9 Racemate
A racemic mixture or racemate is an
equimolar mixture of enantiomers which is
optically inactive because the two components
rotate plane-polarized light equally (same
degree of rotation) but in opposite directions.
Hence it does not give a net rotation of planepolarized light.
Applications of chiral compounds in
daily life.
e.g:


() Dopa is used for treatment of Parkinson’s
disease but (+) dopa is toxic to human.
(S)-Ibuprofen the popular analgesic(the active
ingredient in motrin, advil, and many other
nonaspirin analgesics)
REACTIONS OF ORGANIC
COMPOUNDS
Lecture 7
12.5 Reactions of Organic Compounds
Learning Outcomes:
At the end of the lesson the students should
be able to :
Explain covalent bond cleavage:
homolytic
heterolytic
Types of Covalent Bond Cleavage/Fission
 All chemical reactions involved bond
breaking and bond making.
 Two types of covalent bond cleavage : Homolytic cleavage
 Heterolytic cleavage
a)
Homolytic Cleavage
Occurs in a non-polar bond involving two
atoms of similar electronegativity.
A single bond breaks symmetrically into
two equal parts, leaving each atom with one
unpaired electron.
Formed free radicals.
Example:
X : X
X + X
free radicals
X X
b) Heterolytic cleavage
•
Occurs in a polar bond involving unequal sharing of
electron pair between two atoms of different
electronegativities.
•
A single bond breaks unsymmetrically.
•
Both the bonding electrons are transferred to the more
electronegative atom.
•
Formed cation and anion.
A:B
A:+
B+
anion
cation
A is more
electronegative.
A+ + B:cation anion
B is more
electronegative.
Reaction Intermediates
a) Carbocation
• b) Carbanion
• c) Free Radical
They are unstable and highly reactive.
•
a)
Carbocation
Also called carbonium ion.
A very reactive species with a positive
charge on a carbon atom.
Carbocation is formed in heterolytic
cleavage.
Example :
 
(CH3)3C — Cl
(CH3)3C+ +
Clcarbocation
anion
Chlorine is more electronegative than carbon and the
C—Cl bond is polar.
The C—Cl bond breaks heterolitically and both the
bonding electrons are transferred to chlorine atom to
form anion and carbocation.
b) Carbanion
 is
an anion counterpart
 a species with a negative charge on a carbon
atom.
 Carbanion is formed in heterolytic cleavage.
example:
 
• (CH3)3C — Li
Li+
kation
(CH3)3C- +
carbanion
b)
Free Radical
A very reactive species with an unpaired electron.
Formed in homolytic cleavage.
Examples:
i)
free radicals
– Cl
Cl
uv
Cl● + Cl ●
ii)
C
●C
C
+
●C
iii)
H3C
H
H3C ● + ●H
Lecture 7
12.5 Reactions of Organic Compounds
Learning Outcomes:
At the end of the lesson the students should be
able to:
 State the relative stabilities of primary, secondary
and tertiary free radicals, carbocations and
carbanions.
 Explain the inductive effect of alkyl group
towards the stability of carbocations and
carbanions.
 Define electrophile and nucleophile.
Relative Stabilities of Carbocations,
Carbanions and Free Radicals
Carbocation, carbanion and free radical
can be classified into:
 Primary
 Secondary
 Tertiary
Carbocation Stability
The alkyl groups (electron-releasing group)
stabilise the positive charge on the
carbocation.
The stability of carbocation increases with the
number of alkyl groups present.
Carbocation Stability:
H
H
R
R
H C H < H C R <H C R < R C R
+
+
+
+
Methyl
Primary
Secondary
Tertiary
cation
10
20
30
Increasing stability
Carbanion Stability
o
Alkyl group and other electron-donating
groups destabilise carbanions.
o
Electron withdrawing group (e.g: halogen)
stabilise carbanions through the inductive
withdrawal of electron density
Carbanion Stability:
H
H
R
R
H C H < H C- R < H C R < R C- R
Methyl
anion
Primary
10
Secondary
20
Increasing stability
Tertiary
30
Free-radical stability
The stability of free radical increases as
more alkyl groups are attached to the carbon
atom with unpaired electron.
Free Radical Stability :
R
H
H
H
R
H
C
H C
H
<
<
.
.
methyl
radical
Primary
10
C
.
R
R <R C
. R
Secondary
20
Increasing stability
Tertiary
30
Reagents and sites of organic
reactions
A) Electrophile
 Means ‘electron loving’.
 An electron-deficient species and accepting
electron from an attacking nucleophile.
 Can be either neutral or positively charged
Examples of electrophiles :
• cations such as H+, H3O+, NO2+ etc.
• carbocations.
• Lewis acids such as AlCl3, FeCl3, BF3 etc.
• oxidizing agents such as Cl2, Br2 and etc.
electrophilic sites are molecules with low
electron density around a polar bond
Examples:
ii)
i)
+ + -C = O (carbonyl) ; -C – X (haloalkanes)
iii)
+ -C – OH (hydroxy compounds)
b) Nucleophile
means ‘nucleus loving’
An electron-rich species and electron-pair
donor.
A nucleophile can be either neutral or
negatively charged.
Examples of nucleophiles :
 anions
such as OH-, RO-, Cl-, CN- etc.
 carbanions
( species with a negative charge on
carbon atoms ).
Lecture 7
12.5 Reactions of Organic Compounds
Learning Outcomes:
At the end of the lesson the students should
be able to explain the main types of organic
reactions:
• addition: electrophilic and nucleophilic
• substitution: electrophilic, nucleophilic and free
radical
• elimination
• rearrangement
4 Types of Organic Reactions




Addition
Substitution
Elimination
Rearrangement
I) Addition Reaction
 A reaction in which atoms or groups add to
adjacent atoms of a multiple bond.
 Two types of addition :a)
b)
Electrophilic Addition
Nucleophilic Addition
a)Electrophilic Addition
• Initiated by an electrophile accepting electron
from an attacking nucleophile.
• Typical reaction of unsaturated compounds such
as alkenes and alkynes.
Example :
CH3CH=CH2 + Br2
CCl4
CH3CHBrCH2Br
Room
temperature
electrophile
b)
Nucleophilic Addition
Initiated by a nucleophile, which attacks an
electrophilic site of a molecule.
• Typical reaction of carbonyl compounds.
O
CH3

C CH3 + HCN

CN
CH3 C
OH
CH3
II) Substitution Reaction
 A reaction in which an atom or group in a
molecule is replaced by another atom or group.
 Three types of substitution :a)
free radical substitution.
b)
electrophilic substitution.
c)
nuclephilic substitution.
a) Free-radical Substitution
 Substitution which involves free radicals as
intermediate species.
Example :
CH3CH3 + Cl2
uv light
CH3CH2Cl + HCl
b)
Electrophilic Substitution
Typical reaction of aromatic compounds.
• The aromatic nucleus has high electron density,
thus it is nucleophilic and is prone to
electrophilic attack.
Example:
+ Br2
electrophile
Fe
catalyst
Br + HBr
c)
Nucleophilic Substitution
Typical reaction of saturated organic compounds
bearing polar bond as functional group, such as
haloalkane with alcohol.
Example :
 
CH3CH2Br + OH-(aq)
nucleophile
Δ
CH3CH2OH + Br-(aq)
•
III)
Elimination
Reaction
An atoms or groups are removed from adjacent
carbon atoms of a molecule to form a multiple
bond (double or triple bond).
• Results in the formation of unsaturated molecules.
• Example :
CH3CH2OH
conc. H2SO4 CH2= CH2 + H2O

IV)
Rearrangement Reaction
 A reaction in which atoms or groups in a molecule
change position.
 Occurs when a single reactant reorganizes the bonds and
atoms.
Example :
H
H
C
tautomerisme
C R
H C
H
OH
H
C R
O
Exercises
1.
Explain how the free radicals are formed
in homolytic cleavage.
2. Write an equation for the brominebromine bond cleavage in the bromination
of methane. State the type of bond
cleavage.
3.
Which would you expect to be the
most stable free radical ?
CH2CH3 , (CH3)2 CH , CH3 ,

CH3