Isomerism

Question 1

Isomerism

Answer 1

Occurs when two or more compounds have the same molecular formula but different arrangement of atoms in the molecules

Question 2

Constitutional (structural) isomerism

Answer 2

Constitutional isomers have the same molecular formula but different connectivity of atoms, meaning that their atoms are connected in a different order.

Question 3

3 types of constitutional isomerism

Answer 3

chain isomerism
positional isomerism
functional group isomerism

Question 4

cis-trans isomerism

Answer 4

• Cis-trans isomers arise when there is restricted rotation about a bond or a certain part of a molecule, due to a double bond or a ring structure.
  
  • In alkene, there is restricted rotation of groups joined by C=C bond due to the presence of the π bond.
  • For cis-trans isomerism to occur in alkenes, each carbon atom involved in the double bond must have 2 different groups bonded to it (cis-trans isomerism is not possible if one carbon atom of the double bond bears two identical groups)

Cis-trans isomerism is also possible due to the restricted rotation about  bonds in ring structures.
There must be at least two substituent groups bonded to the ring.

Question 5

Enantiomerism

Answer 5

Enantiomers arise when the molecule is asymmetric, i.e. when it does not have a plane of symmetry
(or centre of symmetry).
A plane of symmetry is defined as an imaginary plane through the molecule that divides it into two
halves, where each half is an exact reflection of the other half. This plane may pass through atoms,
between atoms (bonds), or both. Such a molecule is described as chiral.