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Organic Chemistry Questions and Answers – Enantiomerism | Organic Chemistry Multiple Choice Questions and Answers

(1) Which of the following is the definition for enatiomerism?
[A] A pair of stereoisomers each of which has two chirality centres
[B] A pair of stereoisomers that are not mirror images of one another
[C] A pair of stereoisomers that are non-superimposable mirror images of one another
[D] Any pair of stereoisomers
Answer: A pair of stereoisomers that are non-superimposable mirror images of one another
(2) Which of the following statements is not true regarding pairs of enantiomers?
[A] They have identical boiling points
[B] They rotate plane polarized light in opposite directions
[C] They react at identical rates with chiral reagents
[D] They have identical melting points
Answer: They rotate plane polarized light in opposite directions

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(3) Which of the following statements regarding optical rotation is not true?
[A] All R enantiomers are dextrorotatory
[B] All (+) enantiomers are laevorotatory
[C] All (-) enantiomers rotate plane polarized light in a counter clockwise direction
[D] (+) and (-) enantiomers rotate plane polarized light in opposite directions
Answer: All (-) enantiomers rotate plane polarized light in a counter clockwise direction
(4) How many enantiomers are there of the molecule shown below?

[A] 6
[B] 2
[C] 0
[D] 1
Answer: 0
(5) Which of the following notations is not used to distinguish between pairs of enantiomers?
[A] R and S
[B] E and Z
[C] + and –
[D] D and L
Answer: E and Z
(6) Which among the following is true about enantiomerism?
[A] Assignments of R and S labels and (+) and (–) labels are not connected
[B] The labels R and S refer to different conformers
[C] The labels (+) and (–) are used to distinguish enantiomers
[D] The specific rotation of enantiomers is equal and opposite
Answer: The labels R and S refer to different conformers
(7) Which of the following molecules does not possess enantiomers?
[A] CH3CH2CH2CHBrCH3
[B] CH3CH2CBr2CH3
[C] CH3CHBrCH2CH3
[D] CHBr2CH2CHBrCH3
Answer: CH3CH2CBr2CH3
(8) Which of the following is true of any (S)-enantiomerism?
[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
Answer: It is the mirror image of the corresponding (R)-enantiomer
(9) Which of the following is not true of enantiomers?
[A] boiling point
[B] melting point
[C] specific rotation
[D] density
Answer: specific rotation
(10) In the absence of specific data, it can only be said that (R)–2–bromopentane is which of the following?
[A] dextrorotatory (+)
[B] levorotatory (–)
[C] optically inactive
[D] analogous in absolute configuration to (R)–2–chloropentane
Answer: analogous in absolute configuration to (R)–2–chloropentane

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