Isomers

Question 1

What is a structeral isomer?

Answer 1

Structeral isomers have the same number of each type of atom (same molecular formula) but a different structeral arrangement.

Question 2

What is a stereoisomer?

Answer 2

Stereoisomers have the same molecular formula and the same structural formula but the atoms have a different arrangement in space.

Stereoisomers inclue:

1) Cis-trans or E/Z isomers (these have a C=C bond)
2) Optical isomers (these have an asymmertric carbon atom)

Question 3

What must a molecule have for stereoisomers to exist?

Answer 3

1) a C=C bond

2) two different groups attached to the carbon atoms involed in the double bond

Question 4

What are optical isomers?

Answer 4

Optical isomers are a type of stereoisomers. Optical isomers are non-superimposable mirror images of each other. Optical isomers do not have to contain C=C bonds. They occur when a molecule contains a carbon atom which is attached to four different groups. This carbon atoms is called an asymmetric carbon and it is a chiral centre.

Question 5

How do you distinguish between optical isomers of a compound?

Answer 5

Despite them being chemically identical, you can tell optical isomers apart by their optical activity. One optical isomer will rotate the plane of plane-polarized light clockwise while the other optical isomer will rotate the plane anticlockwise.

A mixture of optical isomers that contains equal amounts of each isomer will not show optical activity as the rotating effect of one optical isomer is cancelled out by the other optical isomer.

Question 6

What problem does optical isomers create for drug manufacturers?

Example?

Answer 6

When chemicals are produced in the lab, equal amounds of each optical isomer are produced so will not be optically active. However, if a chemical is produced by an organism it will be optically active because only on optical isomer is produced.

This is a problem for drug manufacturers because one optical isomer may be beneficial and the other may be harmful.

Example: This was the case with the drug thalidomide. It was introduced in the late 1950s as one optical isomer could relieve the symtoms of morning sickness but the other could cause serious birth defects. It is still used to treat lepracy.

This increases the cost of making drugs becuase the isomers need to be seperated. However it does reduce the chance of side effects from the drug when the unwanted isomer is removed and makes the desiered isomer more affective.

Question 7

How can modern synthesis of pharmaceuticals that contain only single optical isomers be carried out??

Answer 7

1) Using enzymes or bacteria
2) Using chemical chiral synthesis or chircal catalysts
3) Using molecules that have a chiral centre and exist as a single optial isomer such as natural alpha-amino acids and sugars as starting materials. These molecules can be used to procude pharmaceuticals which also contain a single optical isomer