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← IIT-JEE 2012 · Paper 2
ChemistryMultiple correct+4Question 40 of 60

IIT-JEE 2012 · Paper 2, Chemistry question 40

Which of the given statement(s) about N, O, P and Q with respect to M is (are) correct?

Five drawings of 1-chloropropane-1,2-diol, CH₃-CH(OH)-CH(OH)Cl (C1 bears Cl, C2 bears CH₃). M (sawhorse, eclipsed): front C2 with HO upper-left, H right, CH₃ down; back C1 with HO upper-left, H right, Cl down: (1R,2S). N (sawhorse): front C1 with H upper-left, OH right, Cl down; back C2 with HO upper-left, H right, CH₃ down: (1R,2R). O (sawhorse): front C2 with HO upper-left, H right, CH₃ down; back C1 with H left, OH right, Cl up: (1R,2S). P (Newman, C2 in front): front CH₃ top, HO lower-left, H lower-right; back H upper-left, OH upper-right, Cl bottom: (1S,2R). Q (Newman, C2 in front): front CH₃ top, HO lower-left, H lower-right; back HO upper-left, H upper-right, Cl bottom: (1R,2R). SMILES in the order M, N, O, P, Q.
Choose one or more options
Answer and worked solution

Official answer: A, B, C

The compound is CHX3−CH(OH)−CH(OH)Cl\ce{CH3-CH(OH)-CH(OH)Cl}, with stereocentres C1 (bearing Cl) and C2 (bearing CHX3\ce{CH3}). Priorities: at C1, Cl > OH > C2 > H; at C2, OH > C1 > CHX3\ce{CH3} > H.

Configurations read from the drawings.

  • M (C2 in front: HO upper-left, H right, CHX3\ce{CH3} down; C1 behind: HO upper-left, H right, Cl down): (1R,2S).
  • N (C1 in front: H upper-left, OH right, Cl down; C2 behind: HO upper-left, H right, CHX3\ce{CH3} down): (1R,2R).
  • O (same front C2 as M; C1 behind: H left, OH right, Cl up): (1R,2S). This is M with the back carbon rotated 180°.
  • P (Newman, C2 in front: CHX3\ce{CH3} top, HO lower-left, H lower-right; C1 behind: H upper-left, OH upper-right, Cl bottom): (1S,2R).
  • Q (same front as P; C1 behind: HO upper-left, H upper-right, Cl bottom): (1R,2R).

Comparisons with M (1R,2S).

  • (A) N (1R,2R) differs at one centre: a diastereomer, i.e. a non-mirror-image stereoisomer. True.
  • (B) O (1R,2S) is the same molecule in another conformation. True.
  • (C) P (1S,2R) has both centres inverted: the enantiomer. True.
  • (D) Q (1R,2R) is a diastereomer, not identical. False.

(A), (B), (C)

Topics:Optical isomerism and chiralityConformations
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