Question

Question: Classify each pair of compounds as constitutional isomers or identical molecules.

a.

b.

Short answer

Answer

1. The given compounds are identical.
2. The given compounds are constitutional isomers.

Step-by-step solution

Constitutional isomers

Constitutional isomers have the same number of atoms of each element but differ in the connectivities of those atoms.

For example, 1-butene and 2-butene have the same molecular formula $C_4{H}_8$but are completely different in terms of the bonding of atoms.

Constitutional isomers

Identical molecules

Identical molecules have the same molecular formula, sequence, connectivities, and arrangement of atoms in space.

Re-draw the structures

Re-draw the given structures along with the bonds from the given Newman structures. Check for isomerism.

Isomerism in the given compounds

a. Re-drawing the structure from the given Newman projections, you get:

Re-drawn structures

Since the IUPAC names of the two structures are the same, the two compounds are identical.

b. Re-drawing the skeletal structure from the given Newman projections, you get:

Re-drawn structures

Since the given compounds are different in bonding, the compounds are constitutional isomers.