Chemistry - STEREO ISOMERISM Question with Solution | TestHub
Consider the following structures of molecular formula C7H12
X = Number of compounds which are optically active
Y = Sum of total number of products obtained when each compound undergoes catalytic hydrogenation.
Find the sum of X + Y = ?
Answer:
Solution:
(1) cis-3,5-Dimethylcyclopent-1-ene: a plane of symmetry passes through C4 and the midpoint of the C=C bond - achiral. Hydrogenation gives only cis-1,3-dimethylcyclopentane : 1 product.
(2) trans-3,5-Dimethylcyclopent-1-ene: no plane or centre of symmetry - chiral (optically active). Its C2 axis makes the two faces of the double bond equivalent, so H2/Ni gives only trans-1,3-dimethylcyclopentane : 1 product.
(3) 3-Methylcyclopent-1-ene: C3 is attached to H, CH3 and two different ring paths - chiral (optically active). Hydrogenation destroys the stereocentre, giving only methylcyclopentane : 1 product.
(4) 1,3-Dimethylcyclopent-1-ene: C3 is a stereocentre - chiral (optically active). Hydrogenation creates a new stereocentre at C1; addition from either face gives cis- and trans-1,3-dimethylcyclopentane : 2 products.
X = 3 (compounds 2, 3, 4); Y = 1 + 1 + 1 + 2 = 5.
Ans. X + Y = 8
