Chemistry - STEREO ISOMERISM Question with Solution | TestHub
Are the following pairs identical, enantiomers, diastereomers, or constitutional isomers?
(a) 
and 
(b) 
and 
(c) 
and 
(d) 
and 
Options:
Answer:
Solution:
Ans. (A) (a) Diastereomers (b) Identical (c) Constitutional isomers (d) Identical.
Sol. (a) Both are 1,2,3-trimethylcyclohexane: C1 and C2 configurations match (both methyls wedged) while C3 differs (dash vs wedge) : diastereomers.
(b) Both are 1,2,4-trimethylcyclohexane; rotating the right-hand drawing by 120 degrees in the plane of the paper superposes it exactly on the left (wedge, wedge, dash pattern) : identical.
(c) 1,3,5-trimethylcyclohexane vs 1,2,4-trimethylcyclohexane: different substitution patterns : constitutional isomers.
(d) Both are pentamethylcyclohexane with the same CH2 position and the same up/down pattern after a 120 degree in-plane rotation : identical.
