ALKYL HALIDE & ARYL HALIDE

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1 QUESTION BANK--1 ALKYL ALIDE & ARYL ALIDE LEVEL I 1. SN1reaction of alkyl halides lead to (a) Retention of configuration (c) Inversion of configuration 2. The reaction 3 + O 3O + is (a) SN2 (c) SE1 (b) Racemisation (d) None of these (b) SN1 (d) SE2 3. The correct order of reactivity of following compounds in nucleophilic substitution is (i) 25 (ii) 25 (iii) 2 (iv) 3 O (a) (i) (ii) (iii) (iv) (c) (iii) (i) (iv) (ii) (b) (iv) (iii) (ii) (i) (d) (iii) (i) (ii) (iv) 4. Each of the following compounds gives a white ppt. when boiled with alcoholic silver nitrate except (a) Vinyl chloride (b) Methyl chloride (c) Benzyl chloride (d) Allyl chloride 5. SN1 reaction is favoured by (a) Polar solvents (b) More number of alkyl groups on the carbon attached to halogen (c) Low concentration for nucleophile (d) All the three 6. Out of the various possible isomers of 77, containing a benzene ring, the weakest bond is present in 2 (a) (b) (c) (d) 7. SN2 reactions are (a) Stereoselective but not stereospecific (c) Stereospecific but not stereoselective (b) Stereoselective as well as stereospecific (d) Neither stereoselective nor stereospecific

2 QUESTION BANK n-propyl bromide on treatment with ethanolic potassium hydroxide produces (a) Propane (b) Propene (c) Propyne (d) Propanol 9. Aryl halides are less reactive towards nucleophilic substitution reactions as compared to alkyl halides due to: 1. The formation of less stable carbonium ion 2. Resonance stabilization 3. Longer carbon-halogen bond 4. The inductive effect 5. sp 2 -ybridized carbon attached to halogen (a) 1, 2, 3 (b) 2, 4, 5 (c) 2, 5 (d) 4, X and Y are (a) (c) and 3 2 O 32ONa (32O) in both cases x (Major) Y (Major) (b) 3 O 2 5 O 2 5 (d) 3 and O in both cases 11. A solution of (+) -2-hloro-2-phenylethane in toluene racemises slowly in the presence of small amount of Sb5, due to the formation of (a) arbanion (b) arbene (c) Free radical (d) arbocation 12. An S 2 reaction at an asymmetric carbon of a compound always gives N (a) an enantiomer of the substrate (b) a product with opposite optical rotation (c) a mixture of diastereomers (d) a single stereoisomer 13. The bond dissociation enthalpy X in 3X (where X is halogen) follows the order (a) I (b) I (c) I (d) I 14. Which of the following statement regarding the SN1 reaction shown by alkyl halide is not correct? (a) The added nucleophile plays no kinetic role is SN1 reaction (b) The SN1 reaction involves the inversion of the stereochemistry around carbon atom of the substrate (c) The SN1 reaction on the chiral starting material ends up with the racemization of the product (d) The more stable the carbocation intermediate, the faster the SN1 reaction 2

3 QUESTION BANK Which of the following orders regarding the boiling point of the given alkyl chloride is correct? (a) 3(2)3 323 (3)3 (b) 3(2)3 323 (3)3 (c) 3(2)3 323 (3)3 (d) 3(2)3 323 (3)3 16. The major product when 2-bromobutane is treated with ethanolic KO is (a) 2-hydroxybutane (b) butanol (c) 1-butene (d) 2-butene 17. Which of the following reagents is most effective in replacing O group in an alcohol by group? (a) gas (b) oncentarted (c) SO (d) SO2 18. The order of reactivity for the SN2 reaction involving replacement of X by a nucleophile in alkyl halides is (a) (b) (c) (d) The treatment of RMgX with ethyl formate leads to the formation of (a) RO (b) 32OR (c) RO25 (d) 25O 20. Which of the following reactions is highly exothermic? (a) Fluorination of benzene (b) hlorination of benzene (c) ominaton of benzene (d) Iodination of benzene LEVEL II 1. Which of the following is the correct order of decreasing reactivity towards nucleophilic substitution? (a) Vinyl chloride allyl chloride propyl chloride (b) Propyl chloride vinyl chloride allyl chloride (c) Ally chloride vinyl chloride propyl chloride (d) Allyl chloride propyl chloride vinyl chloride 2. The decreasing order of reactivity of: m-nitrobromobenzene (1) 2, 4, 6-Trinitrobromo-benzene (II), p-nitrobromobenzene (III) and 2, 4- Dinitrobromobenzene (IV) towards O ions is (a) I II III IV (b) II IV III I (c) IV II III I (d) II IV I III 3. 1-hlorobutane on reaction with alcoholic potash gives (a) 1-Butene (b) 1-Butanol (c) 2-Butene (d) 2-Butanol

4 QUESTION BANK During debromination of mesodibromobutane, the major compound formed is (a) n-butane (b) 1-butane (c) cis-2-butene (d) trans-2-butene 5. The order of reactivities of the following alkyl halides for a S 2 reaction is N (a) RF R R RI (b) RF R R RI (c) R R RF RI (d) RI R R RF 6. The dipole moment of 3X (where X is a halogen) follows the order (a) 3F 3 3 (b) 3F 3 3 (c) 3F 3 3 (d) 3F hlorination of toluene with excess of chlorine under the condition of light and heat produces (a) o-chlorotoluene (b) p-chlorotoluene (c) benzyl chloride (d) benzotrichloride 8. Which of the following statements is correct? (a) Alkyl halides are more reactive than aryl halides towards nucleophilic substitution reactions (b) Alkyl halides are less reactive than aryl halides towards nucleophilic substitution reactions (c) The presence of an electron-withdrawing substituent at ortho and/or para position decreases the reactivity of nucleophilic substitution of chlorine in the substituted chlorobenzene (d) The replacement of chlorine in chlorobenzene by strong bases proceeds via elimination-addition reaction 9. The Wurtz-Fitting reactions involves (a) two molecules of aryl halides (b) two molecules of alkyl halides (c) one molecule of each of aryl halide and alkyl halide (d) one molecule of each of aryl halide and phenol 10. The order of reactivities of the following alkyl halides for a SN2 reaction is (a) RF R R RI (b) RF R R RI (c) R R RF RI (d) RI R R RF 11. Benzene diazonium chloride can be converted into chlorobenzene by (a) Gattermann reaction (b) Sandmeyer reaction (c) Both (a) & (b) (d) none of these 12. Ethyl bromide reacts with magnesium in dry ether to give a compound (A) which further reacts with methanol to yield (a) Ethane (b) Methane (c) Propane (d) Butane

5 QUESTION BANK In the presence of light and air, chloroform is oxidized to (a) O (b) O2 + (c) OO (d) O2 14. Which of the following statements is not correct? (a) bond in vinylchloride is less polar than in 3 (b) bond in vinyl chloride is stronger than in 3 (c) bond in vinyl chloride is shorter than in 3 (d) Vinyl chloride undergoes nucleophilic substitution more readily than omopropane on reaction with LiAI4 yields (a) Propane (b) exane (c) Propene (d) Propyne 16. A dihalogen derivative X of a hydrocarbon with three carbon atoms in a molecule, reacts with alc. KO giving another hydrocarbon which gives red precipitate with amm. u. X gives an aldehyde when treated with aqueous KO. The compound X is (a) 1, 3-Dichloropropane (b) 1, 2-Dichloropropane (c) 2, 2-Dichloropropane (d) 1, 1-Dichloropropane 17. ydrolysis of acetonitrile with conc. gives (a) 3N (b) 3OO (c) 3ON2 (d) 32OO 18. Alkyl halides can be converted to ethers through (a) Frankland reaction (b) Williamson synthesis (c) Fittig reaction (d) Grignard reaction 19. The correct order of rate of SN2 reactivity of 2O, O3, O and 3OO (a) O O3 3OO 2O (b) 2O O O3 3OO (c) O3 O 3OO 2O (d) 2O 3OO O O3 20. Which of the following reactions do not result in the formation of a new bond? (a) Ullmann reaction (b) Fittig reaction (c) Williamson synthesis (d) Wurtz reaction LEVEL III 1. onsider the following compounds 652 (I), 65 (65) (II), 65(3) (III) and 65(3)(65) (IV) The order of reactivity of these towards nucleophilic substitution by SN1 mechanism is (a) I III II IV (b) IV II III I (c) IV III II I (d) IV II I III 2. Identify in the following reation sequence: Mg (i) 3O A B. dry ether (ii) 2O/

6 QUESTION BANK--6 (a) (b) 2 2 (c) (d) 3. onsider and D respectively are A B D Mg DO 2 Na Na ether Dry Ether Dry Ether and D D and (a) (b) D D and D D and (c) (d) 4. In the reaction of p-chlorotoluene with KN2 in liquid N3, the major product is (a) o-toluidine (b) m-toluidine (c) p-toluidine (d) p-chloroaniline 5. The product in the reaction Me I u eat is (a) Me Me (b) 3 (c) 3 (d) None of these 6. Toluene when treated with 2/Fe, gives p-bromotoluene as the major product because the methyl group 1. is para-directing 2. is m-directing 3. activates the ring by hyperconjugation 4. deactivates the ring (a) 1, 3 (b) 1, 2, 3 (c) 1, 2 (d) none is correct

7 QUESTION BANK Identify the set of reagents/reaction conditions X and Y in the following set of transformations X Pr oduct Y 3 3 (a) X = dilute aqueous NaO, 20 ; Y = /acetic acid, 20 (b) X = concentrated alcoholic NaO, 80 ; Y = /acetica cid, 20 (c) X = dilute aqueous NaO, 20 ; Y = 2/3, 0 (d) X = concentrated alcoholic NaO, 80 ; Y = 2/3, 0 8. The order of reactivity of SN2 reactions shown by isomers of chlorobutane is (a) 3(2)3 323 (3)22 (b) 3(2)3 (3) (c) (3)3 2 (3)3 323 (d) (3)3 (3) The number of isomers of dibromobutane is (a) 4 (b) 5 (c) 6 (d) Arrange (I) (II) (III) (IV) I In increasing order of reactivity in SN1 reations (a) I II III IV (b) I II IV III (c) IV II III I (d) I III II IV 11. (65O) 2O2 653 For the given reaction, B is (3)2 = 2 + A B Anhyd. Al3 (a) umene (b) n-butyl benzene (c) p-ymene (d) (3) The order of reactivities among the following halides (I) (II) (III) towards conversion into alcohols through S 1 reaction is N (a) III II I (b) I II III (c) III I II (d) I III II

8 QUESTION BANK hlorination of toluene in presence of light and heat followed by treatment with aqueous NaO gives: (a) o-resol (b) p-resol (c) 2, 4-Dihydroxytoluene (d) Benzoic acid 14. The products of reaction of alcoholic silver nitrite with ethyl bromide are: 1. Ethyne 2. Ethene 3. Nitroethane 3. Ethyl alcohol 5. Ethyl nitrite (a) 3, 5 (b) 3, 4 (c) 2, 3, 5 (d) 1, Arrange the following compound in order of increasing dipole moment: Toluene (I), m- dichlorobenzene (II), o-dichlorobenzene (III) and p-dichlorobenzene (IV). (a) I IV II III (b) IV I II III (c) IV I III II (d) IV II I III 16. Predict the major product 3 2 / Fe? 3 3 (a) (b) 3 (c) (d) All the three 17. The major product in the reaction AgN 3 2?, is (a) 3 2 N (c) 3 2N (b) 3 2Ag (d) None of these 18. Select the correct product in the reaction Me 3 2 Anhy. Al 3 (a) Me ( ) 3 (b) Me 2 ( ) 3 Me ( ) 3 (c) (d) ( ) 3

9 QUESTION BANK In the following groups I. OAc II. OMe III. OSO2Me IV OSO2F2 The order of leaving group ability is (a) I II III IV (b) IV III I II (c) III II I IV (d) II III IV I 20. Arrange the following halides in the decreasing order of SN1 reactivity: (I) 322 (II) 2 = ()3 (III) 32()3 (a) I II III (b) II I III (c) II III I (d) III II I 3

10 QUESTION BANK--10 KEY ALKYL ALIDE & ARYL ALIDE LEVEL I 1. (b) 6. (a) 11. (d) 16. (d) 2. (a) 7. (b) 12. (d) 17. (d) 3. (d) 8. (b) 13. (a) 18. (b) 4. (a) 9. (c) 14. (b) 19. (a) 5. (a) 10. (d) 15. (a) 20. (a) LEVEL II 1. (d) 6. (c) 11. (c) 16. (d) 2. (b) 7. (d) 12. (a) 17. (c) 3. (a) 8. (a) 13. (d) 18. (b) 4. (d) 9. (c) 14. (d) 19. (c) 5. (d) 10. (d) 15. (a) 20. (c) LEVEL III 1. (b) 6. (a) 11. (c) 16. (b) 2. (c) 7. (b) 12. (c) 17. (c) 3. (d) 8. (b) 13. (d) 18. (a) 4. (b) 9. (c) 14. (a) 19. (b) 5. (b) 10. (a) 15. (b) 20. (c)

11 QUESTION BANK--11 INTS & SOLUTION ALKYL ALIDE & ARYL ALIDE LEVEL - I 1. In SN1 reaction, planar carbocation is formed which can be attacked from both sides by the nucleophile, thus it leads to a racemic (dl) product. (b) 2. Primary alkyl halides mainly react by SN2 mechanism while tertiary alkyl halides by SN1 mechanism. (a) 3. (iii) is most reactive because benzyl carbocation is resonance stabilized. (i) is more reactive than (ii) because bond is weaker than bond. (iv) is least reactive because O3 group is electron releasing and makes nucleophilic attack difficult. Thus the correct order of decreasing reactivity. 4. Vinyl chloride does not give white ppt. with AgNO3 because bond in 2= is stronger. This is because i) is directly linked to sp 2 hybridised carbon ii) of resonance stabilisation (a) 5. (a) 6. In benzyl chloride, bond is weakest and its cleavage give benzyl carbocation which is resonance stabilized. In all the other three isomers, due to resonance bond acquires some partial double bond character and stronger bond. 7. SN2 reactions are stereoselective (because a particular stereoisomer give two stereoisomeric products but one of them is in greater amount or even the exclusion of other) as well as stereospecific (because a particular stereoisomer of the reactant produces a specific stereoisomer of the product). On the other hand, SN1 reactions are neither stereo-selective nor stereospecific. (b) alc. KO 2 K 2O (b) 9. (c)

12 QUESTION BANK O 2 O Na 3 3 O Substitution elimination Sb5 Sb6 (+)-2-hloro-2-phenylethane Planar carbocation Sb 6 ( )2 hloro 2 phenylethane or In this reaction, planar carbocation is formed which can be attacked by from either side to give a racemic product. 12. In SN2 reaction, inversion of configuration occurs and only a single stereoisomer is obtained. 13. The bond dissociation enthalpy X (where X is halogen) I (a) 14. The SN1 reaction may or may not involve the inversion of stereochemistry around carbon atom of the substrate. (b) 15. Larger the branching of hydrocarbon chain, lesser the boiling point. (a) 16. The reaction is 3 ethanolic KO 3 (2E)-but-2-ene (major product) 17. The reagent SO2 is most effective 18. The increase in bulkiness of alkyl group decreases reactivity for the SN2 reaction. (b)

13 QUESTION BANK OO25 + RMgX RO + Mg (O25)X (a) 20. Fluorination of benzene is highly exothermic. (a) LEVEL - II 1. Vinyl chloride is least reactive because bond is stronger and shorter. Allyl chloride is more reactive than propyl chloride because Allyl carbocation formed is more stable (due to resonance) than the propyl carbocation. 2. (b) 3. alc.ko 3 (a) 2 2 K O But 1 ene 4. Addition of 2 to trans-but-2-ene gives meso-2, 3-Dibromobutane. Therefore, debromination of meso -2, 3-Dibromobutane will give trans-but-2-ene. 5. With the decrease in size of halogen, X bond energy increases and therefore reactivity of alkyl halide decreases. 6. The dipole moment of 3X (where X is halogen) follows the order (c) 7. Under the condition of light and heat, chlorination of side chain occurs. 3 2 excess benzotrichloride 8. Alkyl halides are more reactive than aryl halides towards nucleophilic substitution reaction. (a) 9. The Wurtz-Fitting reaction involves one molecule of each aryl halides and alkyl halides. (c)

14 QUESTION BANK Stronger the X bond, lesser the reactivity of the alkyl halides for a SN2 reaction. 11. Gattermann reaction involves reaction of diazonium salt with copper powder in the presence of (or ) while Sandmeyer reaction involves reaction of diazonium salt with u (or u). (c) (a) 3O 25Mg 26 + Mg(O3) Mg Ether O2 Light O Vinyl chloride is less reactive towards nucleophilic substitution reactions because bond in it has partial double bond character due to resonance. LiAl (a) 16. aq. KO [ (O) ] O 2 O 3 2 aq. KO u 3 Ammoniacal red ppt. 3 u 17. 3N on partial hydrolysis yields 3ON2 (c) 18. Williamson synthesis involves reaction of alkyl halides with sodium alkoxides. (b) 19. Stronger nucleophiles react through SN2 at faster rate. O3 is the strongest nucleophile while 2O is the weakest, among the given species. (c) 20. In Williamson synthesis new O bond is formed. (c)

15 QUESTION BANK--15 LEVEL - III 1. The carbocations formed from these halides are 2 (I), + (II), + (III) and (IV) + Since the stability of these carbocations decrease in the order IV II III I (because IV is stabilized by two phenyl groups (resonance) and one 3 group (+I effect and hyperconjugation), II is stabilized by two phenyl groups, III is stabilized by one phenyl and one methyl group while I is stabilized by only phenyl group and therefore, the reactivity (in SN1) also decreases in the same order. i.e. IV II III I You should also note that reactivity towards SN2 reaction is in the reverse order i.e., I III II IV (b) 2. O Mg 3 Mg dry ether O O Mg (A) O O/ 2 from Mg(O) (B) O 2 3 2O Alkyl shift (c) 2 carbocation ydride shift (WagnerMeerwein) (Rearrangement) 3 carbocation (more stable) () 3. bond is weaker than bond so it breaks.

16 QUESTION BANK--16 D OD Mg, ether Mg Na, dry ether Wurtz reaction DOD (A) -Mg(OD) (D) (B) D Na, dry ether Wurtz reaction D D () 4. :N 2 /N3 KN 2, liq N3 196K ( N 3, K) (Benzyne intermediate) N 2 p-isomer N 2 m-isomer The benzyne formed as an intermediate gives a more stable carbanion when the nucleophilic attack by the amide occurs at the m-position than at the p-position. (b) 5. Me I 2u I Me Me Me 2uI This is Ullmann s reaction. (b) 6. Due to hyperconjugation the ring is activated and ortho-para position become positions of maximum electron density. Therefore electrophile ( + ) attack at these positions. (a) onc. alcoholic NaO, (X) Dehydroha logenation (b) 3 2 Aceticacid 20 (Y) 3

17 QUESTION BANK rowding around the centre of reaction decreases rate of reaction. (b) 9. The skeleton of isomers are 2 ; ; ; ; 2 2 ; ( 2 ) (c) 10. First compound is a secondary halide and the other three are tertiary halides. Also the reactivity follow the order: hloride bromide iodide. (a) Benzoyl peroxide Anhyd. Al 3 Anti Markownikoff 's rule (c) 12. This order is based on stability of carbocation formed as intermediate and it is 2 3 allylic. (c) 13. Sunlight O O O 2 3NaO(aq.) 3Na O OO Benzoic acid AgNO NO ONO (Alcoholic) (Major) (Minor) (a)

18 QUESTION BANK (b) 16. Because 3 is electron withdrawing group and is meta directing. (b) 17. (c) 18. Anhyd. Al arbocation (Less stable) 3 1,2ydride shift 3 arbocation (More stable) (a) p-ymene 19. The weaker the base, larger the leaving group ability. The order of acid strength of the conjugate acids is F3SO2O 3SO2O OAc MeO The order of corresponding conjugate base is F3SO2O 3SO2O OAc MeO The same will also be leaving group ability. (b) 20. (c) The order of reactivity through SN1 is The compound II is allylic as well as 2 and hence is most reactive.

Halo Alkanes and Halo Arenes

Halo Alkanes and Halo Arenes alo Alkanes and alo Arenes Short Answer Questions: **1. Write the isomers of the compound having formula C 4 9 Br? Sol. There are five isomers of C 4 9 Br. These are: 2-bromobutane is expected to exhibit