Question

9. C (Z-2-hexene d. They are all of equal stability. Choose the most stable alkene among the following a 1-hexene b. (E)-2-hexene 10. What is the relation between an enantiomer's configuration and its specific rotation? (a) Rcompounds usually are dextrorotatory with few exceptions (b) R compounds always are dextrorotatory. (c) There is no relation. (d) R compounds always are levorotatory 11. How many chiral centers are there in tartaric acid, and how many different stereoisomers exist for this acid? он (a) 2 chiral centers; 2 isomers (b) 1 chiral center; 1 isomer (c) 2 chiral centers; 4 isomers (d) 2 chiral centers; 3 isomers HO. Гон OH tartaric acid 12. Which best defines a meso compound? (a) a molecule with a plane of symmetry and no chiral center () a molecule that can be superposed on its mirror image and that does contain chiral centers (c) a molecule that cannot be superposed on its mirror image even though it has no chiral centers (d) a molecule that has no mirror image 13. Which of the following is optically active? (a) A chiral compound (b) An achiral compound (c) A racemic mixture (d) A meso compound (e) All of these are optically active Use the following three structures to answer questions # 14 and #15 below. CH3 он CH3 н- -он но .н н" "он но H CH3 он CH3 ш П I The relationship between I and II is: (a) same compound (b) enantiomers (c) diastereomers (d) constitutional isomers The relationship between I and III is (a) same compound (b) enantiomers (c) diastereomers (d) constitutional isomers

Answer 1

Answer 9):- Most stable alkene is "option (b)- (E)-2-hexene.

Explanation:- More substituted alkenes are more stable than less substituted alkenes due to hyper conjugation and E -isomers are more stable than Z- isomers because of steric hindrance.

Answer 10):- "option-(c) there is no relation" is correct answer.

Answer 11):- There are two chiral centres and three isomers in tartaric acid. Thus, "option (d)- 2 chiral centres; 3 isomers" is correct answer.

Explanation:- A compound with n- identically substituted chiral centres has 2^(n-1)+ 2^(n-2)/2 isomers. Tartaric acid has 2-chiral centres and thus, three isomers . Two of the three isomers are pair of enantiomers and remaining one is meso-isomer (optically inactive).

mixror cook соон 애 coon н он HD но - н н — И — он - Plane of ОН symm- гсоон , он etry Pair of enantiomes соон. Мео - Hom

isomers of tartaric acid (see fig.)

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Answer 12):- Meso compound is best defined- " a molecule that can be superimposed on its mirror image and that does contain chiral centres". Thus, option (b) is correct answer.

Answer 13):- option (a)- " a chiral compound " is optically active.

Answer 14):- I and II are diasteromers. Option (c) is correct one.

Explanation:- first, we have to convert Newman (staggered ) form of structure (I) into Fischer projection. To do this, first, we have to convert staggered form into eclipsed form ( because Fischer projection is always eclipsed). Then, Newnann eclipsed form is converted into Fischer projection. (See below)

то CH3 но и Ноні -Н - Нох нар на 2 и 1 си, — си, Staggered Abя и си, Eclipsed form CH 3

си: си HoH H н — н H но OH — н ch I (11) II) Diasteromers

Answer 15):- I and III as they are superimposable and thus are identical. Thus, option (a) same compound is correct answer.