18) (--Mandelic acid has a speific rotation of-158° What would be the specific r

Question

18) (--Mandelic acid has a speific rotation of-158° What would be the specific rotation of a solution 18 which contains 40% (-)-mandelic acid and 60% (+)-mandelic add? A) -63° B) +95 C) +63 D)-32 19) Which of the statements below correctly describes an achiral molecule? A) The molecule exhibits optical activity when it interacts with plane-polarized light. B) The molecule has an enantiomer. C) The molecule might be a meso form. D) The molecule has a nonsuperimposable mirror image. E) none of the above 19) 20) Which of the following statements correctly pertains to a pair of enantiomers? 20 A) They rotate the plane of polarized light by differing amounts and in the same direction. B) They have different melting points C) They rotate the plane of polarized light by differing amounts and in opposite directions D) They have the same melting point but they have different boiling points E) They rotate the plane of polarized light by exactly the same amount and in opposite 21. Which of the following ayaloalkane has the lowest ring strain 22. Number of alkyl bromide isomers with formula: CH,B 23. Nunber of asyametrie carbons in 2-aethylayelopentanol (A) ayalopropane (B) cyclobutane (C) ayclopentane (D) ayalohexane (E)aycloheptane (C) 3 (D) 4 (E) 5 (A) 1 (B) 2 (B)1 (C) 2 (D) 3 (E) 4 (A) O 4. R/S Labels of the following chiral compounda are H3 HO. (E) can not bo deternined (C) R,s (D) S,F (B) S,S (A) R,R 5. Number of secondary carbons in the following compounds are: (B) 8,4 (C) 6, 2 (A) 6, 4

Explanation / Answer

18. E (40% of (-) isomer will be cancelled by 40% of (+) isomer the remaining 20% of (+) isomer can turn -158*20/100 = 32 degrees)

19. E

20. E

21. D (Cyclohexane has 0 angle strain due to chair form)

22. D (4 isomers are possible, namely 1-bromobutane, 2-bromobutane, 1-bromo-2-methyl propane and 2-brommo-2-methyl propane)

23. C (because 2 carbon centers have 4 different groups at substituent positions)

24. D

25. E

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