IIT-JEE 2009 · Paper 1 · Chemistry Q12

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ChemistryMultiple correct+4 / -1Question 12 of 60

The correct statement(s) about the compound $\ce{H3C(HO)HC-CH=CH-CH(OH)CH3}$ (X) is(are)

The total number of stereoisomers possible for X is 6

The total number of diastereomers possible for X is 3

If the stereochemistry about the double bond in X is trans, the number of enantiomers possible for X is 4

If the stereochemistry about the double bond in X is cis, the number of enantiomers possible for X is 2

Answer and worked solution

Official answer: A, D

Stereo elements. $\ce{CH3CH(OH)-CH=CH-CH(OH)CH3}$ (hex-3-ene-2,5-diol) has two identical stereocentres (C2, C5) and a C=C that can be cis or trans.

For each geometry, two identical stereocentres give three stereoisomers: an enantiomeric pair (R,R)/(S,S) and a meso form (R,S).
Total: $3+3=6$ stereoisomers. (A) is true.
Enantiomers: for either geometry only the (R,R)/(S,S) pair, i.e. 2. So (C) is false and (D) is true.
(B) is false: the six stereoisomers fall into four sets that are diastereomeric to one another (trans chiral pair, trans meso, cis chiral pair, cis meso), not three.

(A), (D)

Topics:Optical isomerism and chirality Geometrical isomerism

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IIT-JEE 2009 · Paper 1, Chemistry question 12