Chemistry - STEREO ISOMERISM Question with Solution | TestHub
Consider the following structures of molecular formula C8H14
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:
Ans. 8
Sol. (1) cis-3,6-dimethylcyclohex-1-ene: a plane of symmetry passes through the midpoints of the C=C bond and the opposite C-C bond - achiral. Hydrogenation gives only cis-1,4-dimethylcyclohexane : 1 product.
(2) trans-3,6-dimethylcyclohex-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-1,4-dimethylcyclohexane : 1 product.
(3) 1,4-dimethylcyclohex-1-ene: C4 is attached to H, CH3 and two different ring paths - chiral (optically active). Hydrogenation creates a new stereocentre at C1; addition from either face gives cis- and trans-1,4-dimethylcyclohexane : 2 products.
+ 
(4) trans-4,6-dimethylcyclohex-1-ene: no symmetry element - chiral (optically active). The two alkene carbons each become CH2 on hydrogenation, so no new stereocentre forms and only trans-1,3-dimethylcyclohexane results : 1 product.
X = 3 (compounds 2, 3, 4); Y = 1 + 1 + 2 + 1 = 5.
X + Y = 8
