Reaction Mechanism Exercise # 5

REACTION MECHANISM Exercise # 5 1. [Previous Year Questions] Part # I Rate of the reaction is fastest when Z is : O R––C O + Nu R––C Z 2. +Z Nu (A) Cl (B) OCOCH3 (C) OC2H5 Among the following compound which can be dehydrated very easily is ? H3C H3C (A) (B) H3C OH CH3 (D) H3C 4. 5. 6. 7. 8. 9. OH OH (C) 3. (D) NH2 OH H3C CH3 CH3 Tertiary alkyl halides are practically inert to substitution by SN2 mechanism because of (A) steric hindrance (B) inductive effect (C) instability (D) insolubility Elimination of HBr from 2-bromobutane result in the formation of (A) Predominantly 2-butyne (B) Predominantly 1-butene (C) Predominantly 2-butene (D) Equimolar mixture of 1 and 2-butene 2-Methylbutane on reacting with bromine in the presence of sunlight gives mainly ? (A) 1-Bromo-3-methylbutane (B) 1-Bromo-2-methylbutane (C) 2-Bromo-3-methylbutane (D) 2-Bromo-2-methylbutane A reaction involving two different reactants can never be : (A) unimolecular reaction (B) first order reaction (C) second order reaction (D) bimolecular reaction Consider an endothermic reaction X  Y with the activation energies Eb and Ef for the backward and forward reaction, respectively. In general (A) Eb < Ef (B) H = U (C) H < U (D) H > U The decreasing order of the ratio of HCN addition to compounds a to d is (a) HCHO (b) CH3COCH3 (c) PhCOCH3 (d) PhCOPh (A) d > b > c > a (B) d > c > b > a (C) c > d > b > a (D) a > b > c > d CH3Br + Nu–  CH3 – Nu + Br– The decreasing order of the rate of the above reaction with nucleophiles (Nu¯) A to D is : [ Nu¯ = (A)  PhO¯, (B)  AcO¯, (C)  HO¯, (D)  CH3O¯ ] 10. (A) D > C > B > A (B) A > B > C > D (C) B > D > C > A The structure of the major product formed in the following reaction is (D) D > C > A > B NaCN DMF   CH2Cl (A) CN (B)  11. CH2Cl (C) CN CH2CN CH2CN (D)  Which of the following is the correct order of decreasing SN2 reactivity ? (A) RCH2X > R3CX > R2CHX (B) RCH2X > R2CHX > R3CX (C) R3CX > R2CHX > RCH2X (D) R2CHX > R3CX > RCH2X CN 12. 13. Which of the following reactions will yield 2,2-dibromopropane ? (A) CH3 – C  CH + 2HBr  (B) CH3CH = CHBr + HBr  (C) CH  CH + 2HBr  (D) CH3– CH = CH2 + HBr  The organic chloro compound, which shows complete stereochemical inversion during an SN2 reaction, is (A) (CH3)3CCl 14. For a reaction (B) (CH3)2CHCl (C) CH3Cl (D) (C2H5)2CHCl 1 A  2B, rate of disappearance of 'A' related to the rate of appearance of 'B' by the expression. 2 d [ A ] 1 d [B] d [ A ] d [B] d[A] d [B] d [ A ] 1 d [B]   4  (B)  (C)  (D)  dt 4 dt dt dt dt dt dt 2 dt From amongst the following alcohols the one that would react fastest with conc. HCl and anhydrous ZnCl 2, is (A)  15. (A) 2-Butanol (B) 2-Methylpropan-2-ol 16. Consider the following bromides : 17. The correct, order of SN1 reactivity is : (A) B > C > A (B) B > A > C The main product of the following reaction is : (C) 2-Methylpropanol (C) C > B > A (D) 1-Butanol (D) A > B > C conc. H2SO4 C6H5CH2CH(OH)CH(CH3)2   18. 19. 20. 21. 22. 23. (A) (B) (C) (D) Sodium ethoxide has reacted with ethanoyl chloride. The compound that is produced in the above reaction is: (A) Diethyl ether (B) 2-Butanone (C) Ethyl chloride (D) Ethyl ethanoate Consider thiol anion (RS) and alkoxy anion (RO). Which of the following statement is correct ? (A) RS is less basic but more nucleophilic than RO. (B) RS is more basic and more nucleophilic than RO. (C) RS is more basic but less nucleophilic than RO. (D) RS is less basic and less nucleophilic than RO. Which branched chain isomer of the hydrocarbon with molecular mass 72u gives only one isomer of mono substituted alkyl halide ? (A) Tertiary butyl chloride (B) Neopentane (C) Isohexane (D) Neohexane A solution of ( – ) – 1 – Chloro–1–phenylethane in toluene racemises slowly in the presence of a small amount of SbCl5, due to the formation of : (A) carbanion (B) carbene (C) carbocation (D) free radical An unknown alcohol is treated with the “Lucas reagent” to determine whether the alcohol is primary, secondary or tertiary. Which alcohol reacts fastest and by what mechanism : (A) secondary alcohol by SN1 (B) tertiary alcohol by SN1 (C) secondary alcohol by SN2 (D) tertiary alcohol by SN2 In SN2 reactions, the correct order of reactivity for the following compounds : CH3Cl, CH3CH2Cl, (CH3)2CHCl and (CH3)3CCl is : (A) CH3CH2Cl > CH3Cl > (CH3)2CHCl > (CH3)3CCl (B) (CH3)2CHCl > CH3CH2Cl > CH3Cl > (CH3)3CCl (C) CH3Cl > (CH3)2CHCl > CH3CH2Cl > (CH3)3CCl (D) CH3Cl > CH3CH2Cl > (CH3)2CHCl > (CH3)2CCl REACTION MECHANISM 24. The increasing order of the reactivity of the following halides for the SN1 reaction is : CH3CHCH2 CH3 CH 3CH2CH 2Cl Cl (I) 25. p H3CO (II) C 6H 4 CH 2Cl (III) (A) (III) < (II) < (I) (B) (II) < (I) < (III) (C) (I) < (III) < (II) The major product formed in the following reaction is : (D) (II) < (III) < (I) HI Heat I (A) I Part # II 1. 2. 3. 4. 5. OH (B) I (C) OH (D) OH I OH [Previous Year Questions][IIT-JEE ADVANCED] The order or reactivity of phenyl magnesium bromide with the following compounds is : (A) (II) > (III) > (I) (B) (I) > (III) > (II) (C) (II) > (I) > (III) (D) all react with the same rate The major product obtained on acid–catalysed hydration of 2–phenylpropene is : (A) 2-Phenylpropan-2-ol (B) 2-Phenylpropan-1-ol (C) 3-Phenylpropan-2-ol (D) 1-Phenylpropan-1-ol Which is the best reagent to convert cyclohexanol into cyclohexene. (A) conc. HCl (B) conc. HBr (C) conc. H3PO4 (D) HCl + ZnCl2 The acidic hydrolysis of ether (X) shown below is fastest when : (A) one phenyl group is replaced by a methyl group. (B) one phenyl group is replaced by a para-methoxyphenyl group. (C) two phenyl groups are replaced by two para-methoxyphenyl groups (D) no structural change is made to X. Compounds P and R upon ozonolysis produce Q and S, respectively. The molecular formula of Q and S is C8H8O. Q undergoes Cannizzaro reaction but not haloform reaction, whereas S undergoes haloform reaction but not Cannizzaro reaction. (i) P i) O3/CH2Cl 2 ii) Zn/H2O Q (C8H8O) (ii) R i) O3/CH2Cl 2 ii) Zn/H2O The option(s) with suitable combination of P and R, respectively, is(are) S (C8H8O) (A) H3C and H3C (B) H3C CH3 and H3C H3C CH3 (C) CH3 CH3 and CH3 CH3 (D) CH3 and CH3 H3C 6. CH3 H3C H3C For the following compounds, the correct statement(s) with respect to nucleophilic substitution reactions is(are) CH3 CH3 Br Br H3C C Br Br CH3 I II III IV (A) I and II follow SN2 mechanism (B) Compound IV undergoes inversion of configuration (C) The order of reactivity for I, III and IV is : IV > I > III (D) I and III follow SN1 mechanism Paragraph for Q. 7 & Q. 8 The reaction of compound P with CH3MgBr (excess) in (C2H5)2O followed by addition of H2O gives Q. The compound Q on treatment with H2SO4 at 0°C gives R. The reaction of R with CH3COCl in the presence of anhydrous AlCl3 in CH2Cl2 followed by treatment with H2O produces compound S. [Et in compound P is ethyl group] (H3C)3C CO2Et Q R S P 7. 8. The reactions, Q to R and R to S are (A) Friedel-Crafts alkylation and Friedel-Crafts acylation (B) Dehydration and Friedel-Crafts acylation (C) Friedel-Crafts alkylation, dehydration and Friedel-Crafts acylation (D) Aromatic sulfonation and Friedel-Crafts acylation The product S is COCH3 (H3C)3C CH3 (A) H3COC (H3C)3 C H3C CH3 O CH3 (B) HO3S (H3C)3C H3C (C) CH3 (H3C)3 C (D) COCH3 COCH3 REACTION MECHANISM 9. In the following reaction sequence, the correct structure(s) of X is (are) Me 1)PBr3 .Et 2 O  2) Nal,Me 2 CO X  3) NaN .HCONMe 3 2 enatiomerically Pure Me Me (A) (B) (C) (D) Me 10. LIST - I contains reactions and LIST - II contains major products. LIST - I + (P) LIST - II Br OH HBr + (2) OMe + (R) OH (1) ONa (Q) Me OH Br NaOMe (3) Br OMe + (S) MeBr (4) ONa O (5) Match each reaction in LIST-I with one or more products in LIST-II and choose the correct option. (A) P  1, 5 ; Q  2 ; R  3 ; S  4 (B) P  1, 4 ; Q  2, 4 ; R  4 ; S  3 (C) P  1, 4 ; Q  1, 2 ; R  3, 4 ; S  4 (D) P  4, 5 ; Q  4 ; R  4 ; S  3, 4 EXERCISE - 5 : PART # I 1. A 14. A 2. C 15. B 3. A 16. A 4. C 17. A 5. D 18. D 6. A 19. A 7. A 20. B 8. D 21. C 9. D 22. B 10. C 23. D 11. B 24. B 12. A 25. D 13. C 7. 8. 9. 10. B PART # II 1. C 2. A 3. C 4. C 5. B, C 6. A, B, C, D B C B