What is the stereochemical relationship between the following two molecules?a)Identicalb)Geometrical isomersc)Enantiomersd)DiastereomersCorrect answer is option 'A'. Can you explain this answer?

Question

Answer

The given compound, 1,2-dimethylcyclobutane has two chiral centers, and hence, has maximum of 22=4 stereoisomers. However, as shown in the scheme below, the cis-isomer has a plane of symmetry, and as a consequence, it is a meso-isomer:

However, trans-isomer can exists in two forms: (1R,2R)-1,2-dimethylcyclobutane and (1S,2S)-1,2-dimethylcyclobutane (see Scheme

A

).

The two isomers given in the question are both trans-isomers. Thus, they woul be either identical or enanthiomers as shown in the Scheme

A

(cannot be diastereomers). Although, the OP's visualization is correct and can use to identify simple molecule like this, it is hard to visualize if presented complex molecule. The best way to identify stereoisomers are assign their appropriate (R/S)-configurations as I have done for OP's structures (see Scheme

B

).

Accordingly, both structures are (1R,2R)-1,2-dimethylcyclobutane. Thus, the compounds are identical.

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