Chemistry - STEREO ISOMERISM Question with Solution | TestHub
Give the names, structural formulas and stereochemical designations of the isomers of (a) dichlorocyclopropane, (b) bromochlorocyclopropane, (c) dimethylcyclobutane. Indicate chiral C's.
(a) 
(b) 
(c) 
Options:
Answer:
Solution:
(a) Dichlorocyclopropane: 1,1-dichlorocyclopropane - one structure, no chiral carbon. 1,2-Dichlorocyclopropane: cis form is meso ((1R,2S), internal plane through C3 - achiral); trans form is a pair of enantiomers, (1R,2R) and (1S,2S).
(b) Bromochlorocyclopropane: 1-bromo-1-chlorocyclopropane - one structure, no chiral carbon. 1-Bromo-2-chlorocyclopropane: cis and trans forms; because Br and Cl differ there is no internal symmetry, so cis = (1S,2R)/(1R,2S) and trans = (1R,2R)/(1S,2S), each a pair of enantiomers.
(c) Dimethylcyclobutane: 1,1-dimethylcyclobutane - one structure, no chiral carbon. 1,2-Dimethylcyclobutane: cis is meso ((1R,2S)); trans is a pair of enantiomers ((1R,2R)/(1S,2S)). 1,3-Dimethylcyclobutane: cis and trans, both achiral - C1 and C3 are not chiral carbons (the two ring paths at each are identical).
Chiral carbons are the starred ring carbons of the 1,2-isomers.
