Organic Chemistry Multiple Choice Questions on “Diastereomers”.
1. Which of the following is the definition of a pair of diastereomers?
a) A pair of stereoisomers each of which has two chirality centers
b) Any pair of stereoisomers
c) A pair of stereoisomers that are not mirror images of one another
d) A pair of stereoisomers that are non-superimposable mirror images of one another
Answer: c
Clarification: Not all stereoisomers are diastereomers. For example, a pair of molecules which are non-superimposable mirror images of one another are enantiomers, not diastereomers.
2. What is the relationship between given compound?
a) Diastereomer
b) Enantiomer
c) Identical
d) Don’t have any relation
Answer: a
Clarification: Both molecules have the same molecular formula (C9H17Cl) and the same connectivity. Each molecule also has three stereocenters and does not contain a plane of symmetry. Therefore, both molecules are chiral. It can be determined that these molecules are non-superimposable and are not mirror images. Therefore, the molecules are diastereomers.
3. Which of the following is the diastereomer of the following compound?
a) 
b) 
c) 
d) 
Answer: a
Clarification: Both molecules are chiral. It can be determined that these molecules are non-superimposable and are not mirror images. Therefore, the molecules are diastereomers.
4. Which of the following can exist as diastereomers?
a) Lactic acid
b) 1-Butene
c) 2-Butene
d) Ethane
Answer: c
Clarification: The two possible geometries of 2-butene are cis-2-butene and trans-2-butene; cis indicates that substituents are arranged on the same side of the double bond, while trans indicates opposite sides. These are stereoisomers; the atoms are connected in the same way but arranged differently in space.
5. Which structure(s) represent(s) diastereomer(s) of the following compound?
a) 
b) 
c) 
d) 
