Isomerism

Question 1

Define Diastereomerism

Answer 1

Diastereomerism occurs when two or more stereoisomers of a compounds have different configurations at one or more but not all, of the same stereocenters and are not mirror images of each other.

Question 2

Chirality

Answer 2

Chiral molecules cannot be superimposed on their mirror image.

(N.W): Chiral molecules have NO plane of symmetry

Question 3

Information on Enantiomers

Answer 3

Enantiomers are molecules which are mirror images of each other (non-superimposable).

Enantiomers can be identified by rotating the plane of polarized light by equal amounts, and of opposite angles.

Seperating enantiomers occurs by a process called resolution.

Question 4

What is a racemic mixture?

Answer 4

A racemic mixture is when you form two enantiomers of equal amounts, 50:50 mixture ratio.

Question 5

Number of possible isomers?

Answer 5

If there are n stereogenic centers, there are 2^n possible isomers in the molecule.

Question 6

Conformation vs Configurational

Answer 6

Conformation (C-C):
Can be interconverted via rotation of single bond.

Configurational (C=C):
Can NOT be interconverted

Question 7

What are regioisomers?

Answer 7

Regioisomers are stereoisomers in terms of position, this can mean that an alkene group can be disubstituted or trisubstituted

Question 8

What are tautomers?

Answer 8

The interconversion of the two forms involves the movement of an alpha hydrogen and the shifting of bonding electrons

Question 9

Keto Enol Tautomerism

Answer 9

1) Keto form is more stable than enol form.

Question 10

Keto Enol Tautomerism (Excepetions)

Answer 10

Keto is not ALWAYS more stable than enol.

1) Aromatic enol vs Phenol where the enol version (phenol) is MORE stable than the keto version (aromatic enol)
2) Hydrogen bonding in compounds will form stable structures and in this case, enols are also more stable than ketos