Q.59. - Organic Chemistry

Question

Question: Classify each pair of compounds as constitutional isomers, stereoisomers, identical molecules, or not isomers of each other.

a. 

b.

c.

d.

Step-by-Step Solution

Answer

Answer

1. Identical molecules
2. Constitutional isomers
3. Stereoisomers
4. Identical molecules

Step 1: Constitutional isomers

These isomers have the same molecular formula but are different in the bonding of atoms.

For example, ethanol and dimethyl ether have the same molecular formula $C_2{H}_{6}O$ but are completely different in terms of the bonding of atoms.

Constitutional isomers

Step 2: Stereoisomers

The molecular formula and the sequence of bonded atoms are the same in these isomers. These isomers differ only in the spatial arrangement of atoms. 

For example, cis-dichloroethene and trans-dichloroethene have the same molecular formula and sequence of atoms but differ in the spatial arrangement of atoms in three-dimensional space. 

Step 3: Classification of the given compounds

a. In both the structures, the two methyl groups are one carbon apart; one group is up and the other is down. Hence, the two structures are the same. 

Identical molecules

 

b. The molecular formula of both structures is the same, but the connectivities of these groups are different. Hence, the given two structures are constitutional isomers. 

Constitutional isomers

 

c. In the first structure, one of the ethyl groups is up, and the other is down. In the second structure, both ethyl groups are down. Hence, the given two structures with the same molecular formula and sequence differ only in the spatial arrangement of the groups. 

Hence, the given structures are stereoisomers. 

Stereoisomers

 

d. The ethyl and methyl groups in both structures are on the upper side. Hence, the given structures are identical. 

Identical molecules