What is the relationship between the following pairs?

Question

Different MF, identical, conformational isomers, constitutional isomers, configurational isomers

A & B

D & E

C & D

E & C

Bonus: In the most stable conformation of structure A (or B), how many methyl groups (CH3) occupy axial positions and how many occupy equatorial positions?

Answer 1

A & B: Identical isomers. A and B are the same molecule in the same conformation, therefore they are identical.

D & E: Conformational isomers. D and E are different conformations of the same molecule, therefore they are conformational isomers.

C & D: Constitutional isomers. C and D are different molecules with the same molecular formula, therefore they are constitutional isomers.

E & C: Configurational isomers. E and C are different molecules with the same molecular formula, but they have different spatial arrangements and cannot be interconverted without breaking or forming chemical bonds. Therefore, they are configurational isomers.

Bonus: In the most stable conformation of structure A (or B), the distribution of the methyl groups would depend on the specific structure and the position of the substituents. Without further information, it is not possible to determine the exact number of methyl groups in axial and equatorial positions.