Organic Chemistry

An Introduction
Specific Objectives:

Students should be able to:

1. Define the term ‫״‬homologous series‫״‬

2. Write the general and molecular formula for any member of a given homologous
series.

3. State the difference between molecular and structural formula.

4. Draw and name the isomers of alkanes C4H10 to C6H14

What is Organic Chemistry?

Organic Chemistry, also called Carbon Chemistry, is a branch of Chemistry concerned

with the study of carbon-based compounds.

These compounds are called Organic compounds. They form a major part of the bodies
of living organisms and the food we eat. Proteins, carbohydrates and fats are all organic
compounds.
Some useful organic compounds in everyday life
Different types of Formulae
● The fully-displayed structural
● The molecular formula. This shows
formula. This is a 2-dimensional
the actual number of atoms of each
diagram of how the atoms are
element in one molecule of the
compound. The molecular formula of
arranged in one molecule of the
butanoic acid is C4H8O2. compound. The fully-displayed
molecular formula of Butanoic acid
● The condensed structural formula.
is:
This shows the arrangement of the
atoms in a molecule without drawing
a diagram. The condensed molecular
formula of butanoic acid is
CH3CH2CH2COOH
Practice

1. Look up the molecular formula of the following hydrocarbons. Use it to determine

their structural formula and condensed structural formula:
(a) Methane
(b) Ethane
(c) Propane
(d) Butane
Important Definitions

✔ CATENATION – the ability of carbon to bond to itself in many different ways eg.,
straight-chain, branched chain, rings, with single bonds, with double, triple bonds
etc.

✔ HOMOLOGOUS SERIES- a family of organic compounds having the same functional

group eg., alkanes, alkenes, alcohols, carboxylic acids, esters.

✔ FUNCTIONAL GROUP- this is a bond or group of atoms that determine the chemical
properties of the compound.
 CHARACTERISTICS OF A HOMOLOGOUS SERIES

1. All members of the series have the same functional group.

2. All members of the series can be represented by the same general formula.
3. All members of the series can be prepared by the same general method.
4. All members of the series possess similar chemical properties.
5. All members show a gradual change in their physical properties, such as their
molar mass and mpt./bpt increases but density and solubility decreases.
The five homologous series that we will be studying are Alkanes, Alkenes, Alcohols,
Carboxylic acids and Esters.
Homologous General Formula Functional Group Example
Series

Alkane CnH2n+2 C -C Ethane

n≥1

Alkene CnH2n C=C Ethene

n≥2

Alcohol CnH2n+1OH O-H Ethanol

n≥1

Carboxylic Acid CnH2n+1COOH COOH Ethanoic acid

n≥0

Ester CnH2n+1COOCnH2n+1 COO Ethy ethanoate

Review Questions
Answer the following questions:

1. How many bonds can a carbon atom form with other atoms?
2. What is a functional group?
3. Complete the table below.
Compound Homologous Molecular Fully-displayed Condensed
series formula structural formula structural
formula
Pentane alkane
( 5C)
Propene alkene
( 3C)
Propanol alcohol
( 3C)
Propanoic Carboxylic acid
acid ( 3C)
Chemical Nomenclature
General Objective

To understand how to name organic compounds as well as the phenomenon of structural

isomerism.
Specific Objectives:

1. Name the straight alkanes of carbons 1-10.

2. Draw and name molecules that are alkenes, alcohols and carboxylic acid.

3. Define structural isomerism

3. Draw and name isomers of alkanes up to 6 carbons.

Chemical Nomenclature

● This is the process of naming chemical compounds

to ensure that there is no confusion when a person reads the name of a compound.

● The set of rules were developed by the international Union of Pure and Applied
Chemistry, IUPAC
Naming Straight Chain Compounds

● Name has two parts.

➔ First part or prefix tells the total number of carbon atoms present in one
molecule.
➔ Second part tells the homologous series to the compound belongs.
Naming Straight Chain Compounds
Prefixes

Total number of Prefix Total number of Prefix

carbon atoms carbon atoms

1 meth 6 hex

2 eth 7 hept

3 prop 8 oct

4 but 9 non

5 pent 10 dec
Naming Straight Chain Compounds

Ending of name
Homologous series Name ends with

Alkane ane

Alkene ene

Alcohol anol

Carboxylic Acid anoic acid

Example 1

This compound has 5 carbons in a chain.So the first part of its name is called pent (from the table above)

We know its an alkane because it only has C-C bonds. So the last part of its name is ane

Putting these two parts together gives us the name pentane

Example 2

This molecule has 2 carbons in a chain, so the first part of its name is eth
The functional group on the molecule is -OH, which means it is an alcohol. The last part of its name is
therefore -anol
Putting these two parts therefore gives us ethanol.
Example 3

This compound has 3 carbon atoms, so the prefix is prop-

It has the COOH functional group on the right of the molecule. This tells us it is a carboxylic acid. The
ending of its name is therefore -anoic acid
Example 4

This molecule has 2 carbon atoms. So the prefix is eth-

It also has a C=C functional group. This tells us it is an alkene. The last part of its name is -ene.
It is therefore ethene.
Practice

1. Give the names of all the straight-chain alkanes containing from 1-10 carbon atoms.
2. Give the name and condensed structural formula of each of the following straight
chain molecules.
● An alcohol with one carbon:
● An alkene with three carbons:
● A carboxylic acid with three carbons:
Structural Isomerism
Structural Isomerism

Firstly watch this video:https://youtu.be/pg6GWz3zXas

Structural Isomerism

● The occurrence of two or more organic compounds with the same molecular formula
but different structural formulae, ie. they have the same number and type of atoms
but they are arranged differently.
● These molecules are called isomers.
Structural Isomerism

Examples of the Alkane isomers of C4H10: Butane and Methylpropane ( also known as
Isobutane)
Practice

Can you draw the three structural isomers of the alkane C 5H12? They were shown in the
video above.
Answer

View this slide only after you have tried drawing the diagrams on the previous slide.
Practice

Firstly watch this video:https://youtu.be/oUaXduj3xPM

Can you draw the four structural isomers of C6H14? One of them is a straight-chain isomer
and the other four are branched chains.( Make sure that all the four molecules have the
same number of carbon and hydrogen atoms, with each carbon having four bonds around
it. Then simply rearrange the atoms.Note that branches cannot form on the carbon atoms
at the ends of the molecule.
Naming Branched-chain Alkanes
General Objective

To understand how to name branched-chain organic compounds based on their structural

formula.
Specific Objectives

1. State the steps in naming branched-chain alkanes.

2. Give the name and formula of alkyl groups with 1-3 carbon atoms.
3. Name an alkane with more than one branches.
4. Name four branched-chain alkanes.
Naming Branched Chain Organic Compounds

● Firstly watch this video: https://youtu.be/BSpy2HSGbN0

Steps:

● First, find the longest continuous chain of carbon atoms, this is the straight chain.
Name it (last part of name)
● Then number the carbon atoms on the straight chain so that the branch (functional
group) gets the lowest possible number.
● Name the branch
Naming Branched Chain Organic Compounds

● The branches are usually called alkyl groups, with general formula C nH2n+1 and name
ends with ‘yl’

Formula of the alkyl group Name

CH3 methyl

C2H5 ethyl

C3H7 propyl
Naming Branched Chain Organic Compounds

● If there are more than one of the same group, a prefix is placed in front of the name
of the side branch.

Number of the same group prefix

2 di

3 tri

4 tetra
Example 1
1. The longest chain has 6 C
atoms in it. It is the one that
lies horizontal.
2. A substituent/
branch is located at Carbon
number 3. This is the methyl
branch- CH3.
3. The name of the compound
is therefore 3-methylhexane
Example 2

1.This molecule has 4 carbon atoms in the longest

chain (horizontal). The root part of its name is
therefore butane.
2. It has 2 CH3 groups on the second carbon.We
therefore use numbers, separated by commas, to
show their location. We also use the prefix di- to
mean two of them.
The name is therefore: 2,2-dimethylbutane.
Practice
Practice Questions

1. Name the following compounds.

a. C3H6 b. C4H9OH c. CH4

2. Draw the structural formula of 2,3-dimethylhexane

Summary

● Functional Groups
● Alkanes and Alkenes
● Naming Organic compounds