Isomerism

Question 1

Define the term isomer?

Answer 1

Two molecules which have the same molecular formula but the atoms are arranged differently.

Question 2

What are the two types of isomers?

Answer 2

Structural isomers
Stereoisomers

Question 3

What is meant by structural isomers?

Answer 3

Atoms are connected in different ways so they have the same molecular formula ( e.g same number of carbons and same number of hydrogens ) but different structural formulas.

Question 4

Define the term stereoisomerism?

Answer 4

Compounds with the same structural formula
With atoms arranged differently in space

Question 5

What are the three types of structural isomers?

Answer 5

Chain isomers
Positional isomers
Functional group isomers

Question 6

Properties of C=C bonds?

Answer 6

Can’t rotate
Rigid
Restricted rotation ( causes E/Z isomers )
Planar

Question 7

What causes E /Z isomers?

Answer 7

C=C bonds have restricted rotation
Double bond carbons have different atoms or groups attached ( arranged differently )

Question 8

In the Z isomers how are the groups arranged?

Answer 8

Same groups either both above or below the double bond

Question 9

In the E isomers how are the groups arranged?

Answer 9

Same groups arranged across the double bond ( one above and one below )

Question 10

How to use the CIP priority rules to determine E/Z isomers with 4 different groups attached?

Answer 10

Assign priority to two atoms attached to each carbons
Do this by atoms directly bonded to each C=C carbon atom
Atom with higher atomic number is given higher priority. ( things bonded to LHS carbon and things bonded to RHS carbon )
Look to see how the two higher priority groups are arranged
If both above or below ( Z isomer )
If positioned across ( E isomer )

Question 11

Describe how to distinguish between two enantiomers ?

Answer 11

Use plane polarised light
Rotates the plane in opposite directions