C11 INTRODUCTION TO ORGANIC CHEMISTRY

CHEMISTRY UNIT
KOLEJ MATRIKULASI MELAKA

SHARED BY MISS DALINA BINTI DAUD

CHAPTER 11

Introduction to Organic
Chemistry

11.1 Molecular and Structural Formulae
11.2 Functional groups and homologous series
11.3 Isomerisme
11.4 Reaction Of Organic Compounds

11.1 Molecular and Structural Formulae

At the end of the lesson, student should be able
to:

a)define structural formula
b)show structural formula in the form of

expanded, condensed and skeletal structures
based on molecular formula
c) classify carbon into primary, secondary, tertiary
or quaternary and hydrogen into primary,
secondary or tertiary

3

STRUCTURAL FORMULA

Structural formula is a formula that shows how
the atoms of a molecule are bonded to one
another

Expanded
Structure

Skeletal Types of Condensed
Structure Structural Structure
Formula
4

Structural Description Example : C4H9Cl
formula

• Shows all atoms and H HHH

Expanded bonds; bonds are drawn H C C C C Cl

structure as lines

H HHH

• Bonds are not always

Condensed shown; subscripts are CH3CH2 CH2 CH2 Cl
structure
used to indicate the or

number of identical groups

attached to a particular CH3(CH2)3Cl

atom.

Skeletal • Shows the carbon Cl
structure/ skeleton and functional
Bond-line groups 5
formula

Example

Draw the expanded, condensed or skeletal structure for the
followings :

Expanded Structure Condensed Skeletal Structure
Structure

1) (CH3)2CHOH

2)

Cl

3) H H H H H

H CCCC C H
HHHH H

6

Exercise 1

Draw the expanded and skeletal structural formula
for each of the followings :

a) CH3CH2CH(OH)CH2CH2CH3

b) CH3CH(CH3)CH2CH3

c) CH3CO(CH2)2C(CH3)3

d) O

C

H2C CH2

H2C CH2

C(CH3)2 7

Exercise 2
Expand the following bond-line representations to
show all the atoms including carbon and hydrogen

c)
a)

OH

d)

b)

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Exercise 3
Rewrite each of the following structures as skeletal
structural formula.

1. O

CH3CH2 CH2 C CH3 CH CH3

H
2.

H2C CH CH2 CH2C

3. H3C CH2 CH CH2 CH2 C OH

CH3 O
4. (CH3)2CHCH2CH2CH(CH3)CH2CH3

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Answer

Example

Expanded Structure Condensed Skeletal Structure
Structure
H H OH
C OH (CH3)2CHOH
1) H C Cl
(CH3)3CCl
HH C H 10
CH3(CH2)3CH3
H

2) H Cl H

H C C CH
H H C HH

H

3) H H H H H

H CCCC C H
HHHH H

Exercise 1 (answer)

a) H H HH HH H

C CC

C C C H
H O HH
H

H HO

H

b) H H H H
C CH

H CC

HC H H
H

HH

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Exercise 1 (answer)

c) H O H HH H O
C CC
O
H C C C H
H H HC H 12

C

H HH H
H

O

e) H C H

C C
H H
HC
CH

H C HH

CH CH
HH H

Exercise 2 (answer) H

a) H H H H c) H HH C HH
C HC CH
H H H HC H C
H C H C CH
H C C H H
H H
C H H
HH CH
HC CH
HC
H
H
H C
CH

H

H HH d) H O H
C
b) H C H C
H
HC HH C H H H
C CH H C
H
HC

HC CCC HC C
H H HH H H H

H CH

H

13

Exercise 3 (answer)

O

1.

2.

O

3.

OH

4.

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3- Dimensional structural formula H

(wedge and dashed-wedge structure)

HH

H C H C C
Cl H H Cl Cl H

H H
HC
H NOTE : wedge is a bond that
project out of the plane of
the paper

Cl dashed-wedge are bonds

that lie behind the plane

solid lines are bonds that

lie in the plane of the

page 15

Example
Draw the 3 –dimensional structural formula of
bromoethane,

Br
H CH

H

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Answer

H HH

C or H C or C
H H Br Br
HH H
Br

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Classification of carbon and hydrogen atoms in
organic molecules

• In organic molecules, carbon atom can be
classified as primary (1o), secondary (2o),
tertiary (3o) or quaternary (4o) carbon.

• It’s class is depend on the number of other
carbon atoms that are bonded to it.

* Classification of carbon atoms involve only C―C
single bond, C―C multiple bonds cannot be classified

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• Same as carbon atoms, hydrogen atom can
also be classified as primary (1o), secondary
(2o) or tertiary (3o) hydrogen.

• However, it’s class is depend on the class of
carbon at which it is attached to.

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Primary carbon (1oC) and primary hydrogen (1oH)

Atom Description
Carbon 1o Carbon that bonded to one other carbon atom

Hydrogen 1o Hydrogen that bonded to primary carbon

1oH H 1oC

1oH H C CH3
H

1oH

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Secondary carbon (2o C) and Secondary
hydrogen (2o H)

Atom Description
Carbon 2o Carbon that bonded to two other carbon atoms

Hydrogen 2o Hydrogen that bonded to a secondary carbon

2oH 2o C

H

H3C C CH3
H
1oC
2oH

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Tertiary carbon (3oC) and Tertiary hydrogen (3oH)

Atom Description
Carbon 3o
Carbon that bonded to three other carbon
Hydrogen 3o atoms

Hydrogen that bonded to tertiary carbon

3oH 3o C

H

H3C C CH3
CH3

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Quaternary Carbon (4o)

Atom Description
Carbon that bonded to four other
Carbon 4o carbon atoms

Hydrogen -

CH3 4o C

H3C C CH3

CH3

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Exercise
Classify the carbon atoms the following
compounds as 1o, 2o and 3o.
i. CH3 CH3

HO C C NH CH3

H

ii.

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Exercise (answer)

i. 1o 1o 1o

CH3 CH3

HO C 3o C2o NHCH3

H

ii. 2o 3o 2o 3o 1o

2o 1o
2o

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11.2 Functional groups and
homologous series

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11.2 Functional groups and homologous series

At the end of the lesson, student should be able to:
a. define functional group

b. State functional group of the following class of
compounds.

c. identify functional groups in a given compound

d. define homologous series

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11.2 Functional groups and homologous series

At the end of the lesson, student should be able to:
a. explain general characteristics of homologous

series
i. Represented by a general formula
ii. Same functional group and chemical

properties
iii. Gradual change in physical properties with

increasing of carbon atoms
iv. Successive member of a series differ by a –

CH2- group

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Functional group

Functional group is an atom or a group of
atoms in a molecule which determines its

chemical and physical properties.

It serve as :
- a basic for naming organic compounds
- the site of a chemical reaction to occur

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Class Functional General Example
Alkane group Formula
Alkene CH4
Alkyne none CnH2n+2 methane
CnH2n
C=C CnH2n-2 CH2= CH2
(C-C double ethene

bond) CH  CH
CC ethyne
(C-C triple bond)
CH3

Arene CnH2n-6
methylbenzene
(aromatic ring)

Haloalkane/ –X (halogen) CnH2n+1X CH3CH2Cl
Alkyl Halide chloroethane

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Class Functional General Example
group Formula
Alcohol CH3CH2OH
Ether –OH CnH2n+1 OH ethanol
Aldehyde (hydroxyl)
CnH2n+2O CH3OCH3
Ketone – OR methoxymethane
(alkoxy)
CnH2nO CH3C=O
O CnH2nO 
H
CH
ethanal
(carbonyl)
CH3C=O
O 
CH3
C
propanone
(carbonyl)
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Class Functional General Example
Carboxylic group Formula
CH3C=O
acid O CnH2nO2 
OH
acyl chloride C OH
ethanoic acid
Amide (carboxyl)

O CH3C=O

C Cl CnH2n+1COCl 
Cl

(acyl ) ethanoyl chloride

O

CnH2n+1 CONH2 CH3CONH2
Ethanamide
C NH2
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(amide)

Class Functional General Example
Ester group Formula

O CnH2nO2 CH3COOCH3
ethyl ethanoate
CO C

(ester)

Anhydride OO (CnH2n+1 CO)O OO

CO C CH3C O C CH3

anhydride Ethanoic
anhydride

Amine -NH2 (amino) CnH2n+1 NH2 CH3NH2
methanamine

Nitrile CN CnH2n+1 CN CH3CN
ethane nitrile
(cyano)
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EXAMPLE

Consider the following compounds. For each compound,
i. circle and name the functional groups
ii. classify them based on their functional groups

a) CH3 O b) CH3 c)

CH3CCH2C CH3O CH2CH3

CH3 NH2

d) CH2CH3 e) H3C f) H3C
C CHC N
OCH2CH3
O H3C

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EXAMPLE (answer)

Consider the following compounds. For each compound,
i. circle and name the functional groups
ii. classify them based on their functional groups

a) CH3 O

CH3CCH2C amide, amide

CH3 NH2

CH3

b)

carbon-carbon double bond, alkene

c) CH3O CH2CH3 alkoxy, ether

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EXAMPLE

d) CH2CH3

aromatic ring, arene

e) H3C

C OCH2CH3 ester, ester

O

H3C

f) CHC N cyano, nitrile compound

H3C

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Homologous Series

Homologous series are series of
compounds that have the same
functional group whereby each member
differs from the next by a constant

–CH2 unit

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Example

a) Homologus Series of Alkane

i) CH4 C2H6
ii) CH4 + CH2 C3H8 etc..
iii) C2H6 + CH2

b) Homologus Series of Alkene; functional group : C-C double

bond

i) C2H4 C3H6
ii) C2H4 + CH2 C4H8 etc..
iii) C3H6 + CH2

c) Homologus Series of Alkohol ; functional group : hydroxyl

i) CH3OH C2H5OH
ii) CH3OH + CH2 C3H7OH etc..
iii) C2H5OH + CH2

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Some common features of the members of a
particular homologous series are:

 Have the same general formula
 Have the same functional group i.e have the

same chemical properties
 The physical properties change gradually (gas –

liquid – solid) as the number of carbon atoms
increase.
 Successive members of a series differs by a –
CH2 group

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Alkane homologous series

Chemical Structural formula Name
formula
Methane
CH4 CH4 Ethane
Propane
C2H6 CH3 CH3 Butane
Pentane
C3H8 CH3 CH2 CH3 Hexane
Heptane
C4H10 CH3 (CH2)2 CH3 Octane
Nonane
C5H12 CH3(CH2)3 CH3 Decane

C6H14 CH3 (CH2)4 CH3

C7H16 CH3 (CH2)5 CH3

C8H18 CH3 (CH2)6 CH3

C9H20 CH3 (CH2)7 CH3

C10H22 CH3 (CH2)8 CH3 40

 Alkanes and cycloalkanes (alkanes with cyclic
structures) belong to the same class of
compound but different homogous series. Why?

 Both have same functional group, thus they
belong to the same class of compound.

 They have different general formula, thus
they are in different homologous series.
alkane – CnH2n+2
cycloalkane – CnH2n

Cyclo- is a prefix designating a cyclic (ring) compound

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11.3 Isomerism

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11.3 ISOMERISM

At the end of the lesson, student should be able to:
a) define isomerism, constitutional isomerism and

stereoisomerism
b) Identify and construct constitutional isomerism:

i. chain isomer
ii. positional isomer
iii. functional isomer

c) describe cis-trans isomerism due to restricted
rotation about:
i. C=C bond
ii. C-C bond in cyclic compounds

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d) identify cis-trans isomerism of a given structural
formula

e) define chirality center and enantiomers
f) identify chirality centre(s) in a molecule
g) determine optical activity of a compound
h) draw a pair of enantiomers using 3-dimensional

formula

46

Isomerism

The existence of compound with the same
molecular formula but different structural
formulas

Isomers

Compounds that have the same molecular
formula but different structural formulas

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Isomerism

1) Structural/ 2) Stereoisomerism
Constitutional Isomerism

Chain Positional Functional Group diastreomer enantiomer

Isomerism Isomerism Isomerism

cis-trans Other diastreomers
isomerism (Molecule with two

or more chiral car4b8 on)

1. Constitutional isomers

• Different compounds that have the same
molecular formula but differ in their
connectivity, that is, in the sequence in which
their atoms are bonded together.

• It can exist as
a) chain isomers
b) positional isomers
c) functional group isomers

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a) Chain Isomers

 The isomers differ in the carbon skeleton
(different in the longest carbon chain).

 They possess the same functional group and
belong to the same homologous series.

 They have the same chemical properties but
different physical properties

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