Basic Organic Chemistry and Isomerism

Question 1

What are the three types of structural isomer?

Answer 1

• Chain
• Positional
• Functional Group

Question 2

What are chain isomers?

Answer 2

Have different arrangements of the carbon skeleton. Some are straight chains and the others are branched in different ways.

Question 3

What are positional isomers?

Answer 3

Positional isomers have the same skeleton and the same atoms or groups of atoms attached. The difference is that the atom or group of atoms is attached to a different carbon atom.

Question 4

What are functional group isomers?

Answer 4

Have the same atoms arranged into different functional groups.

Question 5

What are stereoisomers?

Answer 5

Have the same structural formula but a different arrangement of atoms in space.

Question 6

Why do E/Z isomers exist?

Answer 6

Because double bonds have a fixed position and you cannot rotate the rest of the molecule around it like a single bond.

Question 7

When do E/Z isomers occur?

Answer 7

When the double bonded carbon atom has two different atoms or groups attached. Then you get and E-isomer and a Z-isomer.

Question 8

What is an E- isomer?

Answer 8

One that has the highest priority groups across the double bond from each other.

Question 9

What is a Z-isomer?

Answer 9

One which has the highest priority groups both above or below the double bond.

Question 10

What is optical isomerism?

Answer 10

Another type of stereoisomerism.
Same structural formula but different arrangement of atoms in space.
Optical isomers have a chiral carbon atom.

Question 11

What is a chiral (or asymmetric) carbon atom?

Answer 11

A carbon atom with four different groups attached.

Question 12

What are optical isomers (enantiomers)?

Answer 12

Mirror images of each other- they cannot be superimposed.

Question 13

Optical isomers are optically active. What does this mean?

Answer 13

They rotate plane-polarised light.

Question 14

What is plane polarised light?

Answer 14

Normal light vibrates in all directions- some of it vibrates up and down, some of it vibrates side to side. If normal light is passed through a polarising filter it becomes plane polarised, this means all the light is vibrating in the same plane.

Question 15

What happens when you pass plane polarised light through an optically active mixture?

Answer 15

The molecules interact with the light and rotate the plane of the vibration of the light. The two enantiomers of an optically active molecule will rotate the plane- polarised light in opposite directions- One clockwise and one anticlockwise.

Question 16

What is a racemic mixture (racemate)?

Answer 16

Contains equal quantities of each enantiomer of an optically active compound.
Don’t show any optical activity- two enantiomers cancel out each others light- rotating effect.
When two molecules react there’s an equal chance of forming each enatiomer.

Question 17

How do drugs work?

Answer 17

They change the chemical reactions that are taking place in the body. Most drugs do this by binding to an active site- usually by binding to an active site- usually an enzyme or a specific receptor molecule.
A drug must be exactly the right shape to fit into the correct active site.
The other enantiomer might fit into a different enzyme, and might cause harmful side effects or have no effect at all.

Question 18

What are the benefits of using a racemic mixture as a drug?

Answer 18

No need to separate which reduces the difficulty and cost of production.

Question 19

What was thalidomide and what were the side effect of thalidomide?

Answer 19

Prescribed to pregnant women for morning sickness- didn’t appear to have any side effects.
Babies began to be born with malformed limbs- thalidomide was shown to be causing these symptoms and use was banned.

Question 20

What was the problem with thalidomide (chemically).

Answer 20

Two optical isomers had different affects on the body. One is an effective anti-sickness drug, the other causes birth defects.
Even if pure dose given of safe isomer the body will convert some into harmful isomer.