isomerism

What is ISOMERS????

ISOMERS ARE COMPOUND WITH

SAME MOLECULAR FORMULA BUT

DIFFERENT STRUCTURAL FORMULA

THAT IS THEY CONTAIN ATOMS OF

THE SAME ELEMENTS BUT THE

ELEMENTS ARE ARRANGED IN

DIFFERENT WAYS.

EXAMPLE :

BUTANE AND METHYL PROPANE ARE ISOMERS.

THEY HAVE THE FOLLOWING CHARACTERISTICS.

IN METHANE ,ETHANE AND PROPANE, THERE IS

ONLY ONE POSSIBLE WAY OF JOINING THE CARBON

ATOMS AND THE HYDROGEN ATOMS.

EACH OF THEM WILL HAVE ONLY ONE

STRUCTURE.ALL OF THEM DO NOT HAVE ANY OTHER

STRUCTURE.

THEREFORE, METHANE,ETHANE AND PROPANE DO

NOT HAVE ISOMERS.

ALL THE ALKANES ABOVE PROPANE HAVE ISOMERS.

THERE ARE 2 DIFFERENT WAYS OF ARRANGING THE

FOUR CARBON ATOMS AND TEN HYDROGEN ATOMS

FOR BUTANE C4H10. THUS BUTANE HAS TWO ISOMERS AS

FOLLOWS :

There are three different ways of arranging the five

carbon atoms and twelve hydrogen atoms for pentane

C5H12

Thus, C5H12 has three isomers.

Examples :

PENTANE

METHYLBUTANE

2,2 DIMETHYLPROPANE

The number of possible alkane isomers

grows rapidly as the number of carbon atoms

increases as shown below :

The IUPAC nomenclature is used to name

alkanes of isomers.

STEP 1 :Find the longest continuous carbon chain in the

molecule.

STEP 2 :Give the name for this longest chain.

STEP 3 :Number the carbon atoms in this longest

chain beginning at the end nearer to the

branches (alkyl groups).The table below

shows the prefixes to name each branch

chain

STEP 4 :Locate and name the attached alkyl

groups.The position of each alkyl group is

given the number of the carbon atoms to

which it is attached on the chain.

{Note : If two or more of the same

kind of alkyl groups are attached to the

same chain, the number of alkyl

groups is indicated by the prefixes

di-(2), tri-(3), tetra-(4) and so on.In

addition, the location of every identical

group must ne indicated by a number.}

STEP 5 :Complete the name for the molecules by

combining the three component part

together.Write the name as a single word.Use

hyphens to separate number and words, and

commas to separate numbers

2,2-Dimethylbutane

A single word . Do not leave any spaces..!

The first two members of the alkene series do not have

any isomer.That is ethene and propene do not have isomers.

All the other members of the alkenes have isomers.

oButene has three isomers

oPentene has five iomers.

Isomerism in alkenes are due to:

oThe changes in the position

of the double bonds.

oThe different arrangements of the

carbon atoms and hydrogen atoms.

Example :

BUTENE, C4H8

By changing the position of the double bond, we have

two isomers.

By rearranging the carbon atoms and the hydrogen

atoms we have another isomer, 2-methylprop-1-ene.

Thus the total number of isomers for C4H8 is three.

The drawing of alkene isomers is similar to

the drawing of alkane isomers. The only

diffrence is the positioning of the double

bond.

STEP 1 :Find the longest continuous carbon chain containing the

double bond.

STEP 2 :Give the name for this longest chain.

STEP 3 :Number the carbon atoms in this longest

chain beginning at the end nearer the double

bond and not nearer to the first alkyl

group.This will ensure the carbon atoms

joined by the double bond have numbers as

low as possible.

(numbering from left to right gives the double

bond the lowest possible number.)

STEP 4 :Locate the double bond by the number of the

first carbon atom in the double bond.This

number is placed infront of the family name.

{NOTE : The position of the

double bond needs to be indicated

only for chains of four or more

carbon atoms.}

CH3

|

CH2=CH - CH - CH3

Double bond is between carbons 1 and 2.

STEP 5 :Locate and name the attached alkyl group.

STEP 6 :Complete the name for the molecule by combining the three

component parts together. Write the name as a single word.

Name of the molecule:

3-methylbut-1-ene.