AtoZ CHEMISTRY Reaction Mechanism Reaction Mechanism (D) have low activation energy compare to that of 1. Introduction to Mechanism & Organic other steps Reaction Q 9. Which of the following is an example of Q 1. In the reaction substitution reaction? O OH −− CN+ CH Br → CH CN + Br + 33 CH3 – C – CH 3 + H / CH 3 OH CH3 – C – CH3 The nucleophile is (A) OCH3 – – (A) CN (B) CH3 (B) CH= CH + HBr → CH − CH Br – 2 2 3 2 (C) Br (D) None of these O O Q 2. In the reaction (C) CH3 – C – Cl + CH3 OH CH33 – C – OCH + HCl H2 C= CH 2 + HBr → CH 3 − CH 2 Br , (D) None of these the electrophile is Q 10. Which of the following reaction is an example of (A) HBr (B) Br– addition reaction ? (C) H+ (D) None of these O O CH – C – Cl + H+ /H O Q 3. Suggest a suitable mechanism for the reaction (A) 32CH3 – C – OH + HCl 2 Br 2A+ 2B → C + D if Rate = KAB H C = CH − CH + Br → CH − CH − CH Q 4. For the exothermic reaction happening in 3 steps 2 3 2 2 3 1. A → B fast (B) Br 2. BC+→ DE+ : slow (C) CH3− CH 2 − OH + H 2 SO 4 ⎯⎯→ CH = 2 CH 2 3. A+→ E 2F ; fast (D) None of these (A) write complete reaction Q 11. Which of the following reaction is an example of (B) Identify the Rds of the reaction elimination reaction? + (C) Draw energy diagram for the reaction H (A)CH3 COOCH 3+ H 2 O ⎯⎯→ CH 3 COOH + CH 3 OH (D) Identify the intermediate species formed (B)CH C H + NaNH ⎯⎯→ CH C C−+ Na + NH Q 5. A and B can react at a certain temperature to give 3 2 3 3 C, the rate controlled product. At a higher (C) temperature they give D, the thermodynamic – CH3 CH 2 CH 2 CHClCH 3+ KOH ⎯⎯→ CH 3 CH 2 CH = CHCH 3 controlled product. Draw the reaction diagram for ++KCl H2 O each cases. (D) None of these Q 6. Kinetically controlled products are formed with Q 12. Which of the following is an example of path having electrohilic addition reaction ? (A) Low Ea (B) high Ea (A) CH3 COOCH 3+ NaOH ⎯⎯→ CH 3 COOH + CH 3 ONa (C) high +ve H (D) high −ve H + (B) CH COCl+ H O ⎯⎯→H CH COOH + HCl Q 7. Thermodynamically controlled products are 3 2 3 formed with (C) CH3 CH= CH 2 + BrCl ⎯⎯→ CH 3 CHClCH 2 Br ((A) Low Ea (B) high Ea (D) None of these (C) high +ve H (D) high −ve H Q 13. Which of the statement is wrong? Q 8. Rds of a reaction mechanism (A) A more stable product is formed at faster rate (A) is much slower compare to other steps (B) A less stable product is formed at slower rate (B) is slower compare to other steps (C) A more stable product is formed at slower (C) have high activation energy compare to that rate of other steps (D) All of these Rishi Sir [B.Tech. IIT Kanpur] www.atozchemistry.com 86 Be Topper with Topper in Chemistry in JEE Main & JEE-ADV Contact No. +91 9852476717 AtoZ CHEMISTRY Reaction Mechanism 2. Substitution Reaction (D) Configuration is lost Q 1. SN1 mechanism involves Q 11. In SN1 reaction generally product is greater than (A) 1 step (B) 2 steps retention product Inversion. It occur when (C) 3 steps (D) None of these (A) Solvent is polar (B) Solvent is non – polar Q 2. SN1 mechanism for the hydrolysis of alkyl (C) Nucleophile is weaker halide involves formation of intermediate (D) Nucleophile is stronger (A) free radical (B) carbocation (C) carbanion (B) None of these Q 12. SNi Reaction Q 3. Which of the following path is not possible on (A) Form retention product SP3 carbon for nucleophilic substitution reaction? (B) a 2nd order reaction (A) First C-L bond is cleaved & then C-Nu bond (C) occur with R–OH with SoCl2 is formed (D) All of the above statements are correct (B) Both C-L bond cleavage & C-Nu bond Q 13. Which of the following reactions is an examples formation occur simultaneously of SN reaction (C) First C-Nu bond is formed & then C-L bond 2 is cleaved (A) CH C− Br + OH−− → CH C − OH + Br ( 33)33( ) (D) All are possible (B) CH CH− Br + OH−− → CH CH − OH + Br ( 33)22( ) Q 4. Transition state of SN2 reaction has −− (C) CH− Br + OH → CH − OH + Br (A) sp2 carbon (B) sp3 carbon 33 23 (D) CH3 CH 2 OH⎯⎯⎯⎯→ H = 2 C CH 2 (C) Both sp &sp characters (−HO2 ) (D) None of these Q 14. Which one of the following statements is wrong Q 5. SN Reaction leads to 1 about SN2 reaction? (A) Reteation of configuration (A) The rate of reaction is independent of the (B) Inversion of configuration concentration of nucleophile (C) Recemisation of configuration (B) Nucleophile attacks the carbon from the side (D) None of these opposite to where the leaving group is attached Q 7. SN2 Reaction is (C) Only in one step the bond formation and bond (A) Endothermic (B) Exothermic breaking takes place (C) Both endothermic & exothermic (D) Rate of reaction [substrate][nucleophile] (D) Neither exothermic nor endothermic Q 15. Arrange the following in order of decreasing tendency towards SN reaction Q 8. SN1 Reaction is 2 (A) Stereospecific (B) Stereoselective CH3 CH 2 CH 2 CH 2 Cl, CH3 CH 2 CHClCH 3 , (C) Regiospecific (D) Regioselective (I) (II) Q 9. SN Reaction is CH CHCH Cl, CH C− Cl 2 ( 32)2 ( 3)3 (A) Stereospecific (B) Stereoselective (III) (IV) (C) Regiospecific (D) Regioselective Q 16. The compound that does not undergo hydrolysis Q 10. SN Reaction on R-configured halide leads to 2 by SN1 mechanism is formation (A) H22 C= CHCH Cl (B) C65 H Cl (A) S-configured carbon (B) R-Configured carbon (C) C6 H 5 CH 2 Cl (D) C6 H 5 CH( C 6 H 5) Cl (C) May be S or R-configuration Rishi Sir [B.Tech. IIT Kanpur] www.atozchemistry.com 87 Be Topper with Topper in Chemistry in JEE Main & JEE-ADV Contact No. +91 9852476717 AtoZ CHEMISTRY Reaction Mechanism 3. SN1, SN2 Reaction (i) CH C− Br (ii) C H CHBr ( 3 )3 ( 65)2 Q 1. Consider the following bromides (iii) C H C CH Br (iv) CH CHBr ( 6 5)2 ( 3 ) ( 3 )2 (A) iv i ii iii (B) ii i iii iv (C) i iii ii iv (D) iii ii i iv The correct order of SN1 Q 8. Consider the reactions, (i) CH CH− CH Br ⎯⎯⎯⎯→C25 H OH (A) I II III (B) II III I ( 32)2 (C) II I III (D) III II I CH CH−+ CH OC H HBr ( 3)2 2 2 5 Q 2. The order of reactivities of the following alkyl − (ii) CH CH− CH Br ⎯⎯⎯→CHO25 halides for a SN2 reaction is ( 32)2 CH CH−+ CH OC H Br− (A) RF RCl RBr RI ( 3)2 2 2 5 (B) RF RBr RCl RI The mechanism of reactions (i) and (ii) are (C) RCl RBr RF RI respectively (D) RI RBr RCl RF (A) SN1 and SN 2 (B) SN1 and SN1 Q 3. An SN reaction at an asymmetric carbon of a 2 (C) SN 2 and SN1 (D) SN 2 and SN 2 compound always gives Q 9. The hydrolysis of 2-bromo-3-methyl butane by (A) an enantiomer of the substrate SN1 mechanism gives mainly (B) a product with opposite optical rotation (A) 3-methyl-1-butanol (C) a mixture of diastereomers (B) 2-methyl-2-butanol (D) a single stereoisomer (C) 2,2-dimethyl-2-propanol Q 4. Which of the following undergoes nucleophilic (D) 2-methyl-1-butanol substitution exclusively by SN1 mechanism? Q 10. In a SN 2 substitution reaction of the type (A) Ethyl chloride (B) Isopropyl chloride −−DMF (C) Chlorobenzene (D) Benzyl chloride R− Br + Cl ⎯⎯⎯→ − R + Cl Br Which one of the following has the highest Q 5. CH Br+ Nu−− → CH Nu + Br 33 relative rate? The decreasing order of the rate of the above (A) CH C− CH Br (B) CH CH Br ( 32)3 32 reaction with nucleophiles Nu− A to D is ( ) (C) CH CH CH Br (D) CH CH− CH Br 3 2 2 ( 32)2 − − − − − [ Nu= ( A) PhO ,( B) AcO ,( C) HO ,( D) CH3 O ] Q 11. Among the molecules (A) DCAB (B) DCBA O22 N−− CH Br CH32−− CH Br I II (C) ABCD (D) BDCA CH O−− CH Br Q 6. Which one is most reactive towards SN 32 1 III reaction? The order of SN2 reactivity is (A) C6 H 5 CH( C 6 H 5 ) Br (A) II III I (B) I III II (B) C6 H 5 C( CH 3)( C 6 H 5 ) Br (C) I II III (D) III II I Q 12. The correct order of SN reactivity in the (C) C6 H 5 CH( CH 3 ) Br 1 molecules (D) C6 H 5 CH 2 Br Q 7. The SN1 reactivity of the following halides will be in the order Rishi Sir [B.Tech. IIT Kanpur] www.atozchemistry.com 88 Be Topper with Topper in Chemistry in JEE Main & JEE-ADV Contact No. +91 9852476717 AtoZ CHEMISTRY Reaction Mechanism CH22= CH − CH − Br , CH2 =− CH Br I II (A) 1 (B) 2 Br (C) Equal rate (D) Can’t predict Q 17.