Question

What is the complete IUPAC name of the following substance ?

• A.
  $(1S,3S)-1-\text{Methylcyclopentane}-1,3-\text{diol}$
• B.
  $(1R,3R)-1-\text{Methylcyclopentane}-1,3-\text{diol}$
• C.
  $(1S,3R)-1-\text{Methylcyclopentane}-1,3-\text{diol}$
• D.
  $(1R,3S)-1-\text{Methylcyclopentane}-1,3-\text{diol}$

Answer 1

The correct option is D

$(1R,3S)-1-\text{Methylcyclopentane}-1,3-\text{diol}$
IUPAC numbering should start from the carbon having both $OH$ and $C{H}_3$ groups.



For $C_1$, the direction of the priority group from 1 to 3 is anti-clockwise. But the least priority group is above the plane so its direction should be reversed (clockwise). Hence, its absolute configuration is R.

Similarly, For $C_3$, the direction of the priority group from 1 to 3 is clockwise. But the least priority group is above the plane so its direction should be reversed (anti-clockwise). Hence, its absolute configuration is S

Therefore, the IUPAC name will be $(1R,3S)-1-\text{Methylcyclopentane}-1,3-\text{diol}$
Hence, option (d) is correct.