Organic Chemistry Questions and Answers – Enantiomers

This set of Organic Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Enantiomers”.

1. Which of the following statements regarding enantiomers not true?
a) All (+) enantiomers are levorotatory
b) All (-) enantiomers rotate plane polarized light in a counterclockwise direction
c) (+) and (-) enantiomers rotate plane polarized light in opposite directions
d) All R enantiomers are dextrorotatory
View Answer

Answer: d
Explanation: This statement is true. (+) and (-) enantiomers rotate plane polarized light in opposite directions.

2. Which of the following is/are the S-enantiomer of alanine?
The following is/are the S-enantiomer of alanine is 2 & 3
a) Only 1
b) Only 2
c) 1 and 3
d) 2 and 3
View Answer

Answer: d
Explanation: 1 and 3 have an S configuration, but 2 has an R configuration. The priority of the substituents on the chirality center of alanine is: -NH2 > -COOH > -CH3 > -H.

3. Would the following compound have an enantiomer.
The following compound have an enantiomer
a) True
b) False
View Answer

Answer: a
Explanation: Yes, this compound has enantiomer because of the steric bulk of the phenyl groups, the molecule would be held in place.
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4. Which of the following is true of any (S)-enantiomer?
a) It rotates plane-polarized light to the right
b) It rotates plane-polarized light to the left
c) It is a racemic form
d) It is the mirror image of the corresponding (R)-enantiomer
View Answer

Answer: d
Explanation: Priorities are assigned to each of the four different groups attached to a given chiral center (one through four, one being the group of highest priority). (It should be understood that each chiral center has to be treated separately.) Orient the molecule so that the group of priority four (lowest priority) points away from the observer. Draw a circular arrow from the group of first priority to the group of second priority. If this circular motion is counterclockwise, it is the S enantiomer.

5. Which of the following is the pair of enantiomer from the following substance?
The following is the pair of enantiomer from the following substance is III & IV
a) I and II
b) II and III
c) III and IV
d) I and V
View Answer

Answer: c
Explanation: Stereocenters, (sometimes called chiral centers) are carbons that have four non-identical substituents on them and are designated as either of R stereochemistry or S stereochemistry. If a molecule has one stereocenter of R configuration, then in the mirror image of that molecule, the stereocenter would be of S configuration, and vice-versa.

6. Is the given pair of compound enantiomers?
The given pair of compound enantiomers in given figure
a) True
b) False
View Answer

Answer: a
Explanation: Stereocenters, (sometimes called chiral centers) are carbons that have four non-identical substituents on them and are designated as either of R stereochemistry or S stereochemistry. If a molecule has one stereocenter of R configuration, then in the mirror image of that molecule, the stereocenter would be of S configuration, and vice-versa.

7. Which of the following is the enantiomer for the following substance?
Find the following is the enantiomer for the following substance
a) The following is the enantiomer for the following substance - option a
b) The following is the enantiomer for the following substance - option b
c) The following is the enantiomer for the following substance - option c
d) The following is the enantiomer for the following substance - option d
View Answer

Answer: a
Explanation: Stereocenters, (sometimes called chiral centers) are carbons that have four non-identical substituents on them and are designated as either of R stereochemistry or S stereochemistry. If a molecule has one stereocenter of R configuration, then in the mirror image of that molecule, the stereocenter would be of S configuration, and vice-versa.
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8. Which of the following molecules exists as a pair of enantiomers?
a) 2-Bromopropane
b) 1-Bromo-3-methylbutane
c) 2-Cyclohexen-1-ol
d) cis-1,2-Dichlorocyclobutane
View Answer

Answer: c
Explanation: 2-Cyclohexen-1-ol can exist as enantiomers as shown below tis compound is called as (1R)-2-Cyclohexen-1-ol.
2-Cyclohexen-1-ol can exist as enantiomers as shown below its compound

9. Which of the following diols exists as a pair of enantiomers?
a) cis-1,3-Cyclohexanediol
b) trans-1,3-Cyclohexanediol
c) cis-1,4-Cyclohexanediol
d) trans-1,4-Cyclohexanediol
View Answer

Answer: b
Explanation: Trans-1,3-Cyclohexanediol exist as enantiomer. (S,S)-cyclohexane-1,3-diol is shown below.
Trans-1,3-Cyclohexanediol exist as enantiomer. (S,S)-cyclohexane-1,3-diol is shown
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10. Which of the following is capable of existing as a pair of enantiomers?
a) 2-methylpropane
b) 2-methylpentane
c) 3-methylpentane
d) 3-methylhexane
View Answer

Answer: d
Explanation: 3-methylhexane exists as a pair of enantiomer. This carbon atom has four non-identical substituents around it, making this carbon a chiral center, and as proof of its chirality the molecule has a non-superimposable mirror image. A fancy term used in textbooks and in the literature to describe molecules that are mirror images of each other is enantiomers, as in “the enantiomer of the left molecule above is the molecule on the right, its mirror image.”
The following is capable of existing as a pair of enantiomers is 3-methylhexane

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