Isomerism

Question 1

What are the two types of isomerism?

Answer 1

strucutral isomerism

stereoisomerism

Question 2

What can stereoisomerism be split into?

Answer 2

geometric isomerism

optical isomerism

Question 3

What is meant by structural isomers?

Answer 3

Molecules with the same molecular formula but different structural formula

Question 4

What are stereoisomers?

Answer 4

molecules with the same molecular formula with a different spatial arrangement of their atoms. Thet are non-superimposable.

Question 5

When does geometric isomerism occur?

Answer 5

in molecules where there is no free rotation about the carbon to carbon bond

Question 6

What does ‘cis’ mean?

Answer 6

on the same side of the fixed bond

Question 7

What does ‘trans’ mean?

Answer 7

on the opposite side of the fixed bond

Question 8

What do geometric isomers sometimes differ in?

Answer 8

their physical and chemical properties

Question 9

Why do some geometric isomers differ in their physical and chemical properties?

Answer 9

due to differences in their ability to pack together

Question 10

What are optical isomers?

Answer 10

non-superimposable mirror images of each other

Question 11

What are molecules which have no symmetry said to be?

Answer 11

chrial

Question 12

If asked to draw an optical isomer, what must you always draw along withit?

Answer 12

the original isomer

Question 13

What are optical isomers also known as?

Answer 13

enantiomers

Question 14

What is a racemic mixture?

Answer 14

a mixture of equal quantities of enantiomers

Question 15

What does light passing through a polarisiting filter vibrate in?

Answer 15

one plane only

Question 16

What hapeens when polarized light passes through a solution containing an optical isomer?

Answer 16

the polarized light is rotated

Question 17

What can the direction of rotation be?

Answer 17

right or left

Question 18

What name is given if the direction of rotation is right?

Answer 18

dextrotatory

Question 19

What name is given if the direction of rotation is left?

Answer 19

laeveorotatory

Question 20

In terms of plane polarised light (ppl), what will enantiomers do?

Answer 20

rotate pple by equal and opposite amounts

Question 21

What effect does a reacemic mixture have on ppl?

Answer 21

it is optically in active and has no effect on ppl

Question 22

What is the angle of rotation denoted by and what is it measured in?

Answer 22

theta and in degrees

Question 23

State 3 properties of optical isomers.

Answer 23

• same physical properties i.e. melting/boiling point
• are often present in equal proportions (racemic mixtures)
• same chemical properties, except when in a chiral environment i.e. when other chiral molecules are present

Question 24

How many optical isomers are normally present in living things?

Answer 24

1

Question 25

What are many medicines and why is this the case?

Answer 25

racemic mixtures because it is too costly to separate the isomers
e.g. Salbutamol - one form is more pharmacologically active
Thalidomide - one enantiomer damaged the unborn baby