Reaction Mechanism Exercise # 2

REACTION MECHANISM Exercise # 2 1. Part # I [Multiple Correct Choice Type Questions] Observe the following reaction and tick correct option (s) r1  ................. (I) r2   CH3 – I + ................. (II) (A) r1 < r2 (B) Transition state in reaction (I) is less stable then transition state in reaction (II) (C) Substrate of both the reactions are equally reactive to a particular nucleophile (D) r1 and r2 both are directly proportional to the concentration of nucleophile CH3ONa 2. (X) (Y). Identify X & Y : (A) X = CH3  CH  CH2 – C  CCH3 | O  CH3 (B) Y = CH3  CH2  CH – C  CCH3 | OCH3 (C) Y = CH 3  CH  CH 2  C  CCH 3 | O  CH 3 (D) X = H2O PCl5   product mixture   3. AgNO 3 Fractional   No. of Fractions ‘n’ . No of product ‘m’ (Total isomers)  distillation (A) Value of m & n are 4,2 respectively. (B) Product mixture, and all fractions are optically active. (C) Value of m & n are 4,4 respectively. (D) Reaction of product mixture with PCl5 is SN2 mechanism. 4. Which of the following reactions represent the major product. (A) (C) CH CH O – 3 2     DMSO H2O   (B) (D) CH CH O – 3 2     DMF 5. 6. Which reaction results in the formation of a pair of enantiomers ? (A) (B) (C) (D) Which of the following reaction will go faster if the concentration of the nucleophile is increased ? (A)  + CH3 (B) (C) (D) + CH3 CH3 SH   +  OH  AcOH + AcO    7. Which is/are correct about alkyl bromide having molecular formula C5H11Br (A) One isomeric alkyl bromide undergoes E1 elimination at the fastest rate (B) Only one is incapable of reacting by the E2 mechanism (C) Only one isomer gives a single alkene on E2 elimination (D) 2-Bromopentane gives the most complex mixture of alkenes on E2 elimination 8. Consider the following E1/SN1reaction : H O 2 Ethanol /  + The missing product (s) is (are) : (A) (B) (C) (D) REACTION MECHANISM 9. Account for the trend in relative rate observed for the formation of alcohol from the alkyl halide in H2O / EtOH at 25ºC. Alkyl Halide Relative rate (i) CH3 – Br 2140 (ii) CH3 – CH2 – Br 171 (iii) 4.99 (iv) 1010 Which of the following statements are true. (A) The first two alkyl halide react mainly by the SN2 pathway (B) The fourth alkyl halide react mainly by the SN1 pathway (C) Water is a poor solvent for alkyl halide so EtOH is added in their solvation (D) Rate of last two can be explain by steric hindrance. 10. 11. Electrophiles are (A) Electron deficent species (C) Electron rich species Which of the followings are nucleophile ? (A) BF3 12. (B) CN– (D) (CH3CH2)3N > (CH3CH2)3P The correct order/s of decreasing reactivity of the given compound towards hydrolysis under identical condition is/are: (A) CH3COCl > CH3CONH2 (B) CH3COCl > (CH3CO)2O (D) (CH3CO)2O > CH3CONH2 Which of the followings give product by SN2 Th mechanism ? (A) (C) 15. (D) NH3 (B) CH3S > CH3SH (C) CH3COOCH3 > CH3COCl 14. (C) OH– The correct nucleophilicity order is/are : (A) CH3 O  > CH3  (C) NH3 > H2O 13. (B) having atleast one pair of electron (D) having vacant p or d-orbital NaOH    PCl 5   NaOH  CH3 – CH2 – OH (B) CH3 – CH2 – Cl   PCl 5   (D) Which of the following reactions is an electrophilic substitution ? Cl   (A) CH3 – I + OH  CH3 OH  I OH  + OH (B) NO2 (C) (D) NO2 + NO2 16. Which of the followings give nucleophilic addition reaction with CH3MgBr : (A) C2H5CHO 17. 18. (B) (C) In which of the following reactions is there a possibility of rearrangement ? (A) SN1 (B) SN2 (C) E1 (A) CF3 – CHCl2 (B) (C) (D) All of these CH=CH–CH3 +  21. (D) E2 E1 cB reaction is given by which of the following in presence of strong base : MeO    19. 20. (D) CH3COOCH3 MeOD CH–CH–CH3 D Br This is an example of which type of elimination reaction ? (A) E1 (B) E1cB (C) E2 (D) SN2 Reaction intermediate of E1cB reaction is : (A) Carbocation (B) Carbanion (C) Benzyne (D) Free radical (C) E1cB` (D) none of these D-exchange is observed in : (A) E1 (B) E2 22. Number of fractions on fractional distillation of solvolysis in ethanol of 1-chlorobut-2-ene is (A) 1 (B) 2 (C) 3 (D) 4 23. Which is the correct reaction coordinate diagram for the following solvolysis reaction ? CH3OH   (A) H . + (B) H Reaction Coordinate (C) H Reaction Coordinate (D) H Reaction Coordinate Reaction Coordinate REACTION MECHANISM acetone + KOH   Product 24. (1R, 3S)–Cis–1–Bromo–3–methylcyclohexane. The product formed in the reaction is (A) (1R, 3S)–Cis–3–methyl cyclohexanol (C) (1S, 3S)–Trans–3–methyl cyclohexanol 25. (B) (1S, 3S)–Cis–3– methyl cyclohexanol (D) (1R, 3R)–Trans–3–methyl cyclohexanol Product Product and mechanism are respectively (A) , SN1 (B) (C) , SN2 (D) Fractional distilatio n  X and Y are : (A) 6 ,6 (B) 9, 5 (C) 9, 6 (D) 6, 4 What is the major product obtained in the following reaction ? NH3   product (A) 28. , SN1 H PO 4 3  Total no. of alkenes (X)     No. of Fractions obtained (Y) 26. 27. , SN2 (B) (C) (D) Consider the following reactions, which are carried out at the same temperature. Et OH CH3 – Br + OH   CH3 – OH + Br DMSO CH3 – Br + OH    CH3 – OH + Br Which of the following statement is correct about these reactions. (A) Both the reactions take place at the same rate (B) The first reaction takes place faster than second reaction. (C) The second reaction takes place faster than first reaction. (D) Both the reactions take place by SN1 mechanism ....(i) ....(ii) H Br Ag  29.  Rearranged Carbocation + AgBr Rearranged carbocation is : + CH3 (A) 30. (B) (C) (D) + Which statement is incorrect about the following reaction : (A) Only one product is formed (B) The product will have walden inversion (C) The reaction mixture will have optical rotation zero (D) The product is a mixture of d +  isomers 31. Which of the following statements are correct for the given alcohol ? – X R – OH  R – X + OH – – – (A) Reaction will not take place because OH is poor leaving group ; X is weak base and OH is strong base – – – (B) Reaction will not take place because OH is poor leaving group ; X is strong base and OH is weak base. – – – (C) Reaction will not take place because OH is strong leaving group ; X is strong base and OH is weak base. – – – (D) Reaction will not take place because OH is good leaving group ; X is weak base and OH is strong base. 32. CH3 – I + K1   (Reaction. I) K2   (Reaction.II) CH3 – I + Which of the following statement is correct. ? (A) Rate of reaction in I is less than reaction II. (B) Rate of reaction in I is more than reaction II. (C) Rate of reaction is equal in both reaction. (D) Rate does not depend upon concentration of nucleophile. 33. Br–CH2–(CH2)2– – Br + CH3NH2  Product Poduct of the reaction is : (A) (B) (C) (D) REACTION MECHANISM 34. CH3CH2OH + HCl CH3CH2Cl + H2O In the above reaction, the leaving group is : (A) 35. (B) H2O NC – CH2 – Br (I) CH3  CH  CH3 | Br (II) (A) II > I > IV > III (B) II > III > I > IV (III) (C) II > I > III > IV CH3 – CH2 – Br (IV) (D) IV > I > II > III Which of the following reactions is the best choice for preparing methyl cyclohexyl ether ? (A) + CH3I  (B) + CH3ONa  (C) (D) 37. (D) The decreasing order of rate of SN2 is : Cl – CH2 – CH2 – Br 36. (C) + CH3I  + CH3OH  Which of the following chloride will exclusively give 2-Methyl but-2-ene on dehydrochlorination by a strong base? (A) 2-Chloro-2-methyl butane (B) 2-Chloro-3-methyl butane (C) 1-Chloro-2-methyl butane (D) None of these SOCl 2    A + SO + HCl 2 Pyridine 38. The product A in the above reaction is (A) (B) (C) (D) 39. Following are the curves for nucleophilic substitution reaction. (I) Potential energy Transition state Reactant Product Reaction coordinate (II) Potential energy Transition state Product Reactant Reaction coordinate (III) Potential energy Transition state - I Reactant Product Reaction Coordinate The correct statement (s) is (are) (A) ‘I’ is potential energy diagram for SN2 reaction that takes place with a negative potential energy change. (B) ‘II’ is potential energy diagram for SN2 reaction with a positive potential energy change (C) ‘III’ shows potential energy diagram for SN1 reaction with large potential energy of activation for first (slowest) step (D) All of the above 40. X and Y are respectively (A) (CH3)2 C=C(CH3)2 and (CH3 )3CCH=CH2 (B) (CH 3 )3CCH=CH 2 and (CH3 )2C=C(CH 3)2 (C) (CH3 )2CH–C(CH 3)=CH2 and (CH3 )2C=C(CH 3)2 (D) (CH3 )2 C=C(CH 3 )2 and (CH3 )2 CH–C(CH 3 )=CH2 REACTION MECHANISM 41. 42. P, Product P is : (A) (B) (C) (D) None (CH3)3C–O–CH2–C6H5 can be prepared from Williamsons synthesis, using : (A) (CH3)3C–Cl and C6H5CH2ONa (B) C6H5CH2Cl and (CH3)3C–ONa (C) (CH3)3C–O–CH2–Cl and C6H5ONa (D) All of these Part # II [Assertion & Reason Type Questions] These questions contains, Statement-I (assertion) and Statement-II (reason). (A) Statement-I is True, Statement-II is True ; Statement-II is a correct explanation for Statement-I (B) Statement-I is True, Statement-II is True ; Statement-II is NOT a correct explanation for Statement-I (C) Statement-I is True, Statement-II is False. (D) Statement-I is False, Statement-II is True. 1. Statement-I : Primary benzylic halides are more reactive than primary alkyl halides towards S N 1 reaction. Statement-II : Reactivity depends upon the nature of the nucleophile and the solvent. 2. Statement-I : Vinylic halides are reactive towards nucleophilic substitution reaction. Statement-II : Reactivity is due to the polarity of carbon-halogen bond. 3. Statement-I : Aryl halides undergo electrophilic substitution less readily than benzene. Statement-II : Aryl halide gives only meta product w.r.t. electrophilic substitution. 4. Statement-I : Iodination of akanes is carried out by heat in presence of readucing agent. Statement-II : Iodination of alkanes takepalce explosively. 5. Statement-I : Chloropropane has higher boiling point than chloroethane. Statement-II : Haloalkanes are polar molecules. Statement-I : Polar solvent slows down SN1 reaction. 6. Statement-II : CH3–Br is less reactive than CH3Cl. 7. Statement-I : Optically active 2-iodibutane on treatment with NaI in acetone undergoes racemisation. Statement-II : Repeated Walden inversions on the reactant and its product eventually gives a racemic mixture. 8. Statement-I : Free radical chlorination of n-butane gives 72% of 2-chlorobutane and 28% of 1-chlorobutane though it has six primary and four secondary hydrogens. Statement-II : A secondary hydrogen is abstracted more easily than the primary hydrogen. 9. Statement-I : Boiling point of alkyl halide increases with increasse in molecular weight. Statement-II : Boiling point of alkylhalides are in the order RI > RBr > RCI > RF. 10. Statement-I : Nucleophilic substitution reaction on an optically active alkyl halide gives a mixture of enantiomers. Statement-II : The reaction occurs by S 1 mechanism. N EXERCISE - 2 : PART # I 1. 9. A, B 2. C, D A, B, C 10. A, D 3. B, C, D 4. A, B, D 5. B, D 6. A, C 11. B, C, D 12. B, C 13. A, B, D 14. A, C 7. A, B, D 15. C, D 8. A, B, C 16. A, C 17. A, C 18. D 19. B 20. B 21. C 22. C 23. B 24. C 25. C 26. C 27. A 28. C 29. B 31. A 32. B 33. C 34. C 35. A 36. A 37. D 38. A 39. D 40. A 41. B 42. B 9. 10. A PART # II 1. B 2. D 3. C 4. D 5. B 6. C 7. A 8. A B 30. D