Question

Which of the following structures represent the same stereoisomer?

• A.
• B.
• C.
• D.

Answer 1

Answer: (A), (D)

Identical stereoisomers will have same absolute configuration at each chiral centres.
The perspective form can be converted to eclipsed saw-horse projection and then to fischer projection to assign R/S configuration.
R/S configuration according to the SIP rule is given below:

Thus, (a) and (d) shows similar configuration. Hence, they are idential.

Also, the identical molecules can be determined by another simple method.
$C-C$ rotation does not affect the R/S configuration of the molecule.
Structure (d) is obtained by simply rotating the respective carbon atom about C-C single bond of structure (a).