Question

29 Give the configurations, respectively, of the following two molecules. CH HO H and CI A. B. C. R and R R and S S and S D. S and R 30 Give the configurations, reypectively, of the folowing two molecules H CH CHy A. B. C. R and R R and S Sand S D. S and R Which one of the following groups has the highest rank as assigned by the Cahn- Ingold-Prelog system for stereogenic (chiral) carbons? 31 A. -CH-CH B. -CH2OH C.-CH-O D. CH SH 32 What is the IUPAC name of the following compound. HC A. (2S, 3S)-2,3-dibromopentane B. (2S, 3R)-2,3-dibromopentane C. (2R, 3S)-2,3-dibromopentane D. (2R, 3R)-2,3-dibromopentane 33 Which of the following statements are true. A. B. C. D. I. If a molecule has a plane of symmetry it is achiral. II. If a molecule has a center of symmetry it is achiral. III. If a molecule has one stereogenic (chiral) center it is chiral. I and II Iand III II and III I, II, and III

Answer 1

29. R and S configuration are based on order of priority of groups attached.

If the movement from 2nd to 3rd priority compound is clockwise it is R configuration and if it is anticlockwise it is S configuration.

3 CH Atumic mass onder -ラ CHE 3 2 anti clocku-ise-

3 Hto back 3
hence the answer is option c , S and S . All other options are incorrect.

30. Here we can see that there are cyclic compounds which are set priorities of according to the group attached which act as tie breaker.

movemunt CH 13 anti dockuise LD C 2 НС. 2

н.с CH 3 anhen CH

ShilhneH to back CAr 1 CH 3 3 2 antclockunse movemnt
hence we can see that both compounds have S confirmation

Therefore option c , S and S is correct. All other options are incorrect.

31. According to Cahnin gold prelog system, highest priority is given to compound with highest mass, and lowest priority to compound with lowest mass

The given compounds are CHCH2 , CH2OH, CHO, CH2SH

Masses are , CHCH2 = 25 , CH2OH = 31 , CHO = 29 , CH2SH = 45

Therefore highest priority = CH2SH

Therefore option D , CH2SH is correct.

32. In this compound there are two stereo centres 2nd and 3rd carbon but in both carbons H is in the front ( or in plane ) we have to shift it backwards to determine configuration. It is shown below for both stereo centres

hence, option D, (2R, 3R)-2,3- dibromopentane is correct answer.

3 H, C Н. С 。.. (.loduns.., nce 3 3 2 mab.

33. Molecules having center of symmetry or plane of symmetry are achiral that is they can be superimposed on their mirror images.

Also, if a molecule have one stereo center then it can be chiral

Hence all the three statements are correct.

Option D (I, II, III ) is correct