ALLKYL HALIDES - Einstein Classeseinsteinclasses.com/Allkyl Halides.pdfHalide exchange (Finkelstein...

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Einstein Classes, Unit No. 102, 103, Vardhman Ring Road Plaza, Vikas Puri Extn., Outer Ring Road

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ALLKYL HALIDES

C1A Physical Properties :

Because of their greater molecular weights, haloalkanes have considerably higher boiling pointsthan alkanes with the same number of carbon atoms.

For a given alkyl group, the boiling point increases with increase of atomic weight of halogen. Sofluoride has lowest boiling point and iodide has the highest boiling point.

With branching boiling point decreases.

Inspite of their modest polarity they are insoluble in water probably because of there inability toform hydrogen bonds.

They are soluble in typical organic solvents of low polarity like benzene, ether, chloroform etc.

Iodo, bromo and polychloro compounds are more dense than water.

Alkane and Alkyl halide compounds of low polarity are held together by vander waal’s forces orweak dipole-dipole attraction.

C1B Method of preparation of Alkyl Halide :

1. From alcohols (Replacement of OH by X) XRROHHXor

PX3

Examples : (a) BrCHCHCHOHCHCHCH 223

heatSOH,NaBror

HBr.conc223

42

(b)

(c)iodideEthyl

23I/P

23 ICHCHOHCHCH 2

Although certain alcohols tend to undergo rearrangement during replacement of –OHby –X, this tendency can be minimized by use to phosphorous halide.

ROH + PCl5 RCl + POCl

3 + HCl

ROH + SOCl2 RCl + SO

2 + HCl

2. Halogenation of Hydrocarbons : HXXRHRh

X2

Examples :

(a) C140,light

Br

0

2

(b) h

Br2

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3. Addition of Hydrogen halides to alkenes :

Peroxide has no effect on HF, HCl and HI

4. Addition of halogen to alkenes and alkynes :

;

5. Halide exchange (Finkelstein reaction) R – X + NaI acetone R – I + NaX (X = Cl, Br)

An alkyl iodide is prepared often from the corresponding bromide or chloride by treatment with asolution of sodium iodide in acetone; the less soluble bromide or sodium chloride precipitate fromthe solution and can be removed by filtration.

6. Hunsdiecker or Borodine-Hunsdiecker reaction :

Silver salts of the carboxylic acids in carbon tetrachloride solution are decomposed bychlorine or bromine to form the alkyl halide e.g.

RCO2Ag + Br

2 RBr + CO

2 + AgBr

The yield of halide is primary > secondary > Tertiary.

7. Swarts Reaction : CH3Br + AgF CH

3F + AgBr

(It is the best way to prepare alkyl florides by halogen exchange)

Practice Problems :

1. An organic halide with formula C6H

13Br on heating with alc. KOH gives two isomeric alkenes (A)

and (B) with formula C6H

12. On reductive ozonolysis of mixture (A) and (B), the following

compounds are obtained :

CH3COCH

3, CH

3CHO, CH

3CH

2CHO and (CH

3)

2CHCHO

The organic halide is :

(a) 2-bromohexane (b) 3-bromo-2-methylpentane

(c) 2, 2-dimethyl-1-bromohexane (d) none of the above

2. Ethene on treatment with bromine in presence of NaCl solution gives :

(a) 1,2-dibromoethane

(b) 1, 2-dichloroethane

(c) a mixture of 1, 2-dibromo and 2- bromo-1-chloro, ethanes

(d) no reaction occurs

[Answers : (1) b (2) c]

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C2 Chemical properties of Alkyl Halides :

(a) Nucleophilic Aliphatic Substitution : When CH3Br is treated with sodium hydroxide in

solvent that dissolves both reagents, there is obtained methanol and sodium bromide. Thisis a substitution reaction : the – OH group is replaced by – Br in the original compound.An alkyl halide is converted into alcohol.

CH3 : Br + –:OH CH

3 – OH + : Br–

It is clearly heterolytic. This is one example of the class of reactions called nucleophilic substitutionreaction.

Nucleophilic substitution is characteristic of alkyl halide.

As halide ion are weak bases. As hydrogen halides show high acidity that is its readiness to release H+

ions so halide ions are weak bases and just a halide releases a proton, so it readily releases carbonagain to other bases.

Basic, electron rich reagents that tend to attack the nucleus of carbon are called nucleophic reagentsor simply nucleophiles.

When this attack result in substitution it is called nucleophilic substitution reaction.

Nucleophile can be neutral with electropair like : NH3, or it can be negatively charged.

If :Z is neutral then R : +Z will be positively charged. If –:Z is negatively charged then R : Z will be

neutral. Nucleophilic substitution is possible by two mechanisms 21 NNSandS .

Reactions of Alkyl Halides : ( 2NS ) (Nucleophilic Substitution)

[R-X, X – I, – Cl, –Br, R CH3–, 10, 20]. Examples of Nucleophilic Substitution are as follows :

(i) R : X + : Z R : Z + –:X (ii) R : X + –OH ROH + :X–

(iii) R : X + H2O ROH (iv) R : X + –:O R ROR’ (Williamson’s Synthesis)

(v) RX + –:C C R R – C CR (vi) RX + – R – M+ R – R’

(vii) RX + I– Acetone RI + X– (viii) RX + KCN RCN + KX

Alkyl iodide Alkyl cyanide

(ix) RX + AgCN AgX + R – NC (x) RX + RCOO– R’COOR + X–

Alkyl isocyanide Ester

(xi) RX + :NH3 R – NH

2 NRNRNHR 4

RX3

RX2

RX

Primary amine

(xii) R – X + (xiii) RX + KSH RSH

(xiv) RX + KSR RSR (xv) R – X + Ar – H + AlCl3 Ar – R (Alkyl benzene)

Thio ether (sulfilde) Friedal Craft reaction

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(b) Dehydrohalogenation :

Elimination

)Minor(322

)Major(33

KOH.alc

OHHC/KOHor32|

3 CHCHCHCHCHCHCHCHCHHCHCCH52

Br

Elimination mechanism is possible in two ways i.e., E1 and E

2 :

E1

E2

1. Rate law expression is r = k[RX] Rate law expression is r = k[RX] [B–]

2. First order reaction Second order reaction

3. Intermediate is carbocation Transition state is formed

4. Order of reactivity of RX Order of reaction of RX

30 > 20 > 10 30 > 20 > 10

5. RI > RBr > RCl > RF RI > RBr > RCl > RF

overall summary of 2N1NE,S,E,S 21 reactions

CH3X Biomolecular reactions i.e., 2N

S only

(Methyl halide)

RCH2X Gives mainly 2N

S reaction

(10)

With hindered strong base [e.g., (CH3)

3CO–] then gives mainly

E2

Gives mainly 2NS with weak bases (I–, CN–, RCO

2–) and mainly

E2 with strong bases like RO–.

Gives mainly 1NS /E

1 or E

2

No 2NS Reaction

In water solvent gives 1NS /E

1

Lower temperature 1NS is favoured

When a strong base (e.g. RO–) is used E2 predominates.

Following are the examples based on 21 NNS,S , E

1 and E

2.

(1) CH3CH

2CH

2Br + CH

3O–

OHCH

C50

3

0

(2) CH3CH

2CH

2Br + (CH

3)

3CO–

COH)CH(

C50

33

0

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(3) OHCH

C50

3

0

(4) (CH3CH

2)

3CBr + OH–

OHCH

C50

3

0

+ CH3O C(CH

2CH

3)

3

(5) (CH3CH

2)

3CBr

OHCH

C25

3

0

(c) Praparation of Grignard reagent :

R – X + Mg ether

R – MgX

(d) Reduction :

R – X + M + H+ RH + M+ + X–

e.g. (CH3)

3 – C – Cl

Mg(H

3C)

3C MgCl

OD2 (CH3)

3CD

(e) Wurtz Reaction :

2R – X etherdry/Na R – R + NaX.

(both molecules of alkyl halides can be used different)

(f) Wurtz Fittig Reaction :

etherdry + 2 NaBr

(g) Fittig Reaction :

etherdry

+ 2 NaBr

(h) Reduction by metal and acid

R – X + Zn + H+ R – H + Zn2+ + X—

Example :

(i) 4R – X + LiAlH4 4R – H + LiX + AlX

3[X F]

R – X + —:H RH + —:X [H:— comes from LiAlH4]

LiAlH4 can reduces 10 and 20 alkylhalide

(j) R – X + n(– C4H

9)

3 SnH RH + (n – C

4H

9)

3SnX

Tributyl tin hydride

[It can reduce 10, 20 and 30 alkyl halide].

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(k) Coupling of alkyl halides with organomettalic compounds – (Corey-house alkane synthesis)

Already discussed in Hydrocarbons.

Practice Problems :

1. The non-reactivity of chlorine atom in CH2 = CH — Cl is due to

(a) inductive effect (b) resonance stabilization

(c) electromeric effect (d) electronegativity

2. Which of the following is most reactive towards nucleophilic substitution reactions ?

(a) CH3CH = CHCl (b) CH

2 = CHCl

(c) CH2 = CHCH

2Cl (d) none of these

3. 1-Bromopropane and 2-bromopropane on treatment with sodium in presence of ether gives

(a) n-hexane

(b) 2, 3-dimethylbutane

(c) 2-methylpentane

(d) a mixture of all these different alkanes

4. Compound C4H

8Cl

2(A) on hydrolysis gives a compound C

4H

8O (B) which reacts with hydroxylamine

and does not give any test with tollen’s reagent. What are (A) and (B).

(a) 1, 1-dichlorobutane and butanal (b) 2, 2-dichlorobutane and butanal

(c) 1, 1-dichlorobutane and butan-2-one (d) 2, 2-dichlorobutane and butan-2-one

5. Secondary butyl chloride on boiling with alcoholic potash gives

(a) only 1-butene (b) only 2-butene

(c) isobutylene (d) a mixture of 1-butene and 2-butene

6. Aryl halides are less reactive towards nucleophilic substitution reaction as compared to alkyl halidesdue to

(a) the formation of less stable carbonium ion

(b) resonance stabilization

(c) longer carbon-halogen bond

(d) inductive effect

7. C8H

18 (A) is chlorination forms only one type of C

8H

17Cl(B). Hence A can be :

(a) (b)

(c) (d)

8. ACHBr)CH(Li)1(

BrCHCH)CH()3(CuI)2(23

223

. This is Corey-House method of synthesis of A which is A ?

(a) (CH3)

2CHCH

2CH(CH

3)

2(b) (CH

3)

2CHCH

2CH

2CH

3

(c) (CH3)

2CHCH

2CH

2CH

2CH

3(d) none is correct

9. + Mg AOH

COether

3

2

A is :

(a) (b)

(c) (d)

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10. Major product in the following reaction is : —Br + KOCH2CH

3

(a) — OCH2CH

3(b)

(c) (d)

11. . Which are correct statements :

(a) reactivity for 1NS reaction is I < III < II

(b) reactivity for 2NS reaction is I < II < III

(c) reactivity for 1NS reaction is I > II > III

(d) reactivity for 2NS reaction is I > II > III

12. Major product of the following 1NS reaction is : 523

CH|

Br|

3 HCOCHHCHCCH

3

(a) (b)

(c) (d) none is correct

13.

Increasing tendency for 1NS and 2N

S reaction is :

(A) 1NS : 1 < III < II < IV (B) 2N

S : IV < II < III < I

(a) A and B both are correct (b) only A correct

(c) only B correct (d) both incorrect

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14. C25

ethanol

0 In this reaction :

(a) 2-ethoxy-2-methyl butane is the major product in the absence of ethoxide ion

(b) mixture of 2-methyl-2-butene and 2-methyl-1-butene is the major product in presence ofethoxide ion

(c) both are correct

(d) none is correct

15. + AOH 2NS

A is :

(a) (b)

(c) both (d) none

16. A halide, C5H

11X, on treating with alc. KOH gives only pentene-2. What is structure of halide ?

(a) (b)

(c) (d) both (a) and (c) are correct

17. An alkyl halide (X) of formula C6H

13Cl on treatment with potassium tertiary butoxide gives two

isomeric alkenes (Y) and (Z) of formula C6H

12. Both alkenes on hydrogenation give 2,

3-dimethylbutane. Predict (X).

(a) (b)

(c)

(d)

[Answers : (1) b (2) c (3) d (4) d (5) d (6) b (7) d (8) a (9) a (10) b (11) d (12) c (13) a (14) c (15) b(16) d (17) a]

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SINGLE CORRECT CHOICE TYPE

1. Which one of the following will produce a primaryalcohol by reacting with CH

3MgI

(a) acetone (b) methyl cyanide

(c) ethylene oxide (d) ethyl acetate

2. Grignard reagent adds to :

(a) C = O (b) — C N

(c) C = S (d) all of these

3. Only two isomeric monochloro derivatives arepossible from :

(a) ethane

(b) 2, 2-dimethyl pentane

(c) neopentane

(d) 2-methylpropane

4. When ethyl bromide is treated with dry silveroxide, we get

(a) diethyl ether (b) ethanol

(c) ethane (d) ethene

5. )B()A(CHOCCl2Cl

lightSun

NaOH3

. The

product (B) can be used as :

(a) fire extinguisher (b) solvent

(c) insecticide (d) all above

6. )C()B(CHCCH)NaOH(

CHCl

)HgSO(

SOH.dil3

3

4

42

Compound (C) can be used as :

(a) an anaesthetic (b) an insecticide

(c) a solvent (d) hypnotic

7. CH3Br can be prepared by :

(a) CH3COOAg + Br

2

(b) CH4 + NBS

(c) both

(d) none

8. Order of hydrolysis of the following in increasingorder is :

(a) I < II < III < IV

(b) I < IV < II < III

(c) II < IV < III < I

(d) I < II < IV < III

9.

Increasing tendency for 1NS and 2N

S reaction is :

(A) SN 1 : 1 < III < II < IV

(B) SN 2 : IV < II < III < I

(a) A and B both are correct

(b) only A correct

(c) only B correct

(d) both incorrect

10. C25

ethanol

0 In this reaction :

(a) 2-ethoxy-2-methyl butane is the majorproduct in the absence of ethoxide ion

(b) mixture of 2-methyl-2-butene and 2-methyl-1-butene is the major product inpresence of ethoxide ion

(c) both are correct

(d) none is correct

11. End product of following sequence of reaction :

—Br CBA BaOOH/ONH 233

(a) = O

(b) —OH

(c) = O

(d)

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12. For the reaction,

42SOH

(a) CH3 – CH = CH – CH

3 predominates

(b) CH2 = CH – CH

2 – CH

3 predominates

(c) Both are formed in equal amounts

(d) The product ratio is dependent on thehalogen X

13. Which of the following does not react with benzenein presence of anhydrous AlCl

3

(a) C6H

5Cl

(b) C6H

5CH

2Cl

(c) CH3Cl

(d) C6H

5CH

2CH

2CH

2Cl

14. The alkyl halide which does not give whiteprecipitate with alcoholic AgNO

3 solution is

(a) Ethyl chloride

(b) Allyl chloride

(c) Isopropyl chloride

(d) Vinyl chloride

15. Which chloroderivative of benzene among thefollowing would undergo hydrolysis most readilywith aqueous NaOH to furnish the correspondinghydroxy compound.

(a)

(b)

(c)

(d)

16. The replacement of chlorine from chlorobenzeneto give phenol requires a drastic condition, but thechlorine of 2, 4-dichloronitro benzene is readilyreplaced since

(a) nitro groups make the aromatic ringelectron rich at ortho/para positions

(b) nitro groups withdraw electrons from themeta position of the aromatic ring

(c) nitro groups donate electrons at metaposition

(d) nitro groups withdraw electrons fromortho/para positions of the aromatic ring

17. ClHC3

.3OH.2

KCN.1

A263

Hence A is :

(a) 1, 1 dichloro propane

(b) 1, 2 dichloro propane

(c) 2, 2 dichloro propane

(d) 1, 3 dichloro propane

18. + AOH 2NS

A is :

(a)

(b)

(c) both

(d) none

19. In the following case configuration about chiralC(*) is retained :

(a) BrCHNa 3

(b)

ONaCHTsCl 3

(c)

ONaCHPCl 35

(d) in none case

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20.

A and B are :

(a) in both cases

(b) in both cases

(c)

and

(d)

and

21. The product (A), (B) and (C) are respectively

)C()B()A(HC2I

NaOHHydrolysisHBr42

(a) CH3CH

2Br, CH

3CH

2OH, CHI

3

(b) CH3CH

2Br, CH

2 = CH

2, HCOONa

(c) CH3CHBr

2, HC CH, HCOONa

(d) CH3CBr

3, HC CH, CHI

3

22. RCl is treated with Li in ether to form R — Li,R — Li reacts with water to form isopentane.R — Cl also reacts with sodium to form 2,7-dimethyl octane. The structure of R — Cl is

(a)

(b) CH3CH

2CH

2CH

2Cl

(c)

(d) None

23. With alkali C3H

6Cl

2 (A) gives (B). (B) reacts with

dilute H2SO

4 containing mercuric sulphate to give

C3H

6O (C) which gives idoform test. The possible

structure of A is

(a)

(b)

(c)

(d) All are possible

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24. Identify the product (A) in following reactionseries,

)Y()X(CNCH HNOOHHC/Na3

252

)A()Z(reagent

s'Tollen]O[

(a) CH3CHO

(b) CH3CONH

2

(c) CH3COOH

(d) CH3 – CH

2 – NHOH

25. Identify ‘Z’ in the following reaction series,

)X(BrCHCH.CHheat

OAlNaOH.aq223

32

)Z()Y( OH/Cl 22

(a) Mixture of and

(b)

(c)

(d)

26. CH2 = CHCl reacts with HCl to form

(a) CH2Cl – CH

2Cl

(b) CH3 – CHCl

2

(c) CH2 = CHCl . HCl

(d) None of these

27. What mass of isobutylene from 37 g of tertiary butylalcohol by heating with 20% H

2SO

4 at 363 K, if the

yield is 65%

(a) 16 g (b) 18.2 g

(c) 20 g (d) 22 g

28. What effect should the following reasonance ofvinyl chloride have on its dipole moment ?

lCCHHClCHCCH 22

(a) Decreases

(b) Increases

(c) Remains constant

(d) cannot be predicted

29. With alcoholic potash C3H

7Br (A) gives C

3H

6 (B).

(B) on oxidation gives C2H

4O

2(C) + carbon dioxide

and water. With hydrobromic acid gives (D), anisomer of (A). The compounds (A) and (D) are re-spectively.

(a) ,

(b) ,

CH3 – CH

2 – CH

2Br

(c) Both have same structure i.e.CH

3CH

2CH

2Br

(d) Both have same structure i.e.

ANSWERS (SINGLE CORRECTCHOICE TYPE)

11. c

12. a

13. a

14. d

15. a

16. d

17. c

18. b

19. a

20. c

1. c

2. d

3. d

4. a

5. d

6. d

7. a

8. d

9. a

10. c

21. a

22. a

23. d

24. c

25. b

26. b

27. b

28. b

29. a

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EXCERCISE BASED ON NEW PATTERN

COMPREHENSION TYPE

Comprehension-1

A 10 g mixture of isobutane and iso butene requires20 g of Br

2 (in CCl

4) for complete addition. If 10 g

of the mixture is catalytically hydrogenated and theentire alkane is monobrominated in the presenceof light at 1270C.

1. Total amount of isobutane formed when 10 g of theoriginal mixture is catalytically hydrogenated

(a) 7.25 g (b) 3 g

(c) 10.25 g (d) 0.25 g

2. Which exclusive product is formed after thebromination of the entire alkane ?

(a) BrHCHCCH 2|

3

3CH

(b) BrCCH

3CH

3CH

|

|3

(c) CH3CH

2CH

2CH

2Br

(d)32

|3 CHHCHCCH

Br

3. How much of above exclusive product is formed(Atomic weight of bromine = 80).

(a) 24.21 g (b) 2.36 g

(c) 24.03 g (d) none

(a)

Comprehension-2

A primary alkyl halide (A), C4H

9Br, reacted with

alcoholic KOH to give compound (B). Compound(B) reacted with hydrogen bromide to give (C), anisomer of (A). When (A) was treated with sodium,it gave a compound (D), C

8H

18, which was different

from the compound produced when n-butylbromide was reacted with sodium.

4. Thus ‘A’ is

(a) BCHHCCH 2

|

3

3CH

(b) CH3CH

2CH

2CH

2Br

(c) (CH3)

3CBr

(d) none

5. Thus ‘B’ is

(a) (CH3)

2C = CH

2

(b) CH3CH = CHCH

3

(c) CH3CH

2CH = CH

2

(d) none

6. Thus ‘C’ is

(a) BCHHCCH 2

|

3

3CH

(b) CH3CH

2CH

2CH

2Br

(c) (CH3)

3CBr

(d) none

7. Thus ‘D’ is

(a) (CH3)

2CH(CH

2)

2CH(CH

3)

2

(b) CH3(CH

2)

6CH

3

(c) (CH3)

3C – C(CH

3)

3

(d) none

MULTIPLE CORRECT CHOICE TYPE

1. Benzyl chloride (C6H

5CH

2Cl) can be prepared from

toluene by chlorination with

(a) SO2Cl

2(b) SOCl

2

(c) Cl2

(d) NaOCl

2. Which of the following would give yellow ppt withI

2/NaOH ?

(a) I CH2COOCH

3

(b) CH3COO CO CH

3

(c) CH3CONH

2

(d) CH3CH(OH)CH

2CH

3

3. –Cl x x can be

(a) Et2N (b) KNH

2

(c) alcoholic KOH (d) N2H

4

4. In the haloform reaction, the function of bleachingsuspension is

(a) as a chlorinating agent

(b) as an oxidising agent

(c) as a hydrolysing agent

(d) none

5. The products of reaction of alcoholic silvernitritewith ethyl bromide are

(a) Ethyne (b) Ethene

(c) Nitroethane (d) Ethylnitrite

6. Arylhalides are less reactive than alkyl halidestowards nucleophillic substitution reaction ?because

(a) the formation of less stable carbocation

(b) longer (C–H) bond

(c) Resonance stabilization

(d) sp2 hybridised carbon attached tohalogen

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7. A compound on warming with I2 and aq. NaOH,

iodoform and sodium succinate are formed. Theformula of the compound should be

(a) CH3COCH

2CH

2CH

3

(b) CH3COC

6H

5

(c) CH3COCH

2CH

2COOH

(d) CH3COCH

2CH

2COCH

3

8. R – CH2 – CCl

2 + x R – C C – R, x reagent are

(a) HCl in H2O

(b) KOH in C2H

5OH

(c) NaNH2 in liq. NH

3

(d) Zn and alcohol

9. Which of the following on treatment with NaNH2

in liquid NH3 gives m-anisidine

(a) o-Bromoanisole

(b) m-Bromoanisole

(c) p-Bromoanisole

(d) all the three

10. In , the bonds are formed by

(a) head on overlap of p-orbitals

(b) sidewise overlap of p-orbitals

(c) sidewise overlap of sp2 orbitals

(d) head on overlap of sp2 orbitals

11. I. II.

III.

Which of the following statements are correct :

(a) reactivity for 1NS reaction is I < II < III

(b) reactivity for 2NS reaction is I < II < III

(c) reactivity for 1NS reaction is I > II > III

(d) reactivity for 2NS reaction is I > II > III

Assertion-Reason Type

Each question contains STATEMENT-1 (Assertion)and STATEMENT-2 (Reason). Each question has4 choices (A), (B), (C) and (D) out of which ONLYONE is correct.

(A) Statement-1 is True, Statement-2 is True;Statement-2 is a correct explanationfor Statement-1

(B) Statement-1 is True, Statement-2 is True;Statement-2 is NOT a correctexplanation for Statement-1

(C) Statement-1 is True, Statement-2 is False

(D) Statement-1 is False, Statement-2 is True

1. STATEMENT-1 : n-Butyl chloride has higher b.pt.than n-Butyl bromide.

STATEMENT-2 : C-Cl bond is more polar thanC-Br bond.

2. STATEMENT-1 : Halogens deactive the benzenering, yet o-, p-directing.

STATEMENT-2 : In arylhalides, the electronwithdrawing inductive effect is opposed byelectron releasing resonance effect.

3. STATEMENT-1 : A small amount of ethylalcohol is usually added to chloroform bottles.

STATEMENT-2 : Ethyl alcohol increases the an-aesthetic action or chloroform.

4. STATEMENT-1 : The p-isomer of Dichlorobenzene has higher m.pt. than O- and m-isomer.

STATEMENT-2 : p-isomer is symmetrical, caneasily pack closely in crystal lattice.

5. STATEMENT-1 : Haloarenes are insoluble inwater but are soluble in benzene.

STATEMENT-2 : “Like dissolves like”.

6. STATEMENT-1 : Alkyl halides gives cyanideswith KCN but isocyanides with AgCN as theproduct.

STATEMENT-2 : KCN is predominately ionicwhile AgCN is covalent.

7. STATEMENT-1 : Benzyl chloride undergoesnucleophilic substitution much more readily thanCH

3Cl.

STATEMENT-2 : The intermediate carbocationformed in case of substitution of benzyl chlorideis less stable than in case of CH

3Cl.

8. STATEMENT-1 : The reaction of vinyl chloridewith HI to give 1-chloro-1-iodoethane is anexample of anti-Markovnikov’s rule.

STATEMENT-2 : Anti-Markovnikov additiontakes place in presence of peroxide.

9. STATEMENT-1 : The dipole moment of CH3F is

greater than CH3Cl.

STATEMENT-2 : The C-F bond length (1.38 Å) issmaller than C-Cl bond length (1.77 Å)

CAH – 15


New Delhi – 110 018, Ph. : 9312629035, 8527112111

(Answers) EXCERCISE BASED ON NEW PATTERN

COMPREHENSION TYPE

1. c 2. b 3. a 4. a 5. a 6. c

7. a

MULTIPLE CORRECT CHOICE TYPE

1. a, c 2. a, d 3. a, b, c 4. a, b, c 5. c, d 6. c, d

7. c, d 8. b, c 9. a, b 10. b, c 11. a, d

ASSERTION-REASON TYPE

1. D 2. A 3. C 4. A 5. A 6. A

7. C 8. B 9. D

INITIAL STEP EXERCISE

(SUBJECTIVE)

1. (a) Give simple test to distinguish amonghexane and CH

3 — CH = CHCl.

(b) Give simple test to distinguish amongCH

3 — CH = CHCl, CH

3CH

2CH

2Cl and

CH2 = CH — CH

2Cl.

2. Given reasons for the following :

(a) Potassium cyanide reacts with R — X togive alkyl cyanide, while silver cyanideforms as isoscyanide as a major product.

(b) Silver nitrite reacts with R — X to give amixture of nitroalkane and alkyl nitrite.

(c) ROH does not react with NaBr but onadding H

2SO

4, it forms RBr.

3. A halide, C5H

11X, on treating with alc. KOH gives

only pentene-2. What is structure of halide ?

4. A white precipitate was formed slowly when AgNO3

is added to a compound (A) with molecular formulaC

6H

13Cl. Compound (A) on treating with hot

alcoholic KOH gave a mixture of two isomericalkenes (B) and (C) having formula, C

6H

12. The

mixture of (B) and (C) on ozonolysis furnished fourcompounds.

(i) CH3CHO,

(ii) C2H

5CHO,

(iii) CH3COCH

3,

(iv) (CH3)

2CHCHO

What are (A), (B), and (C) ?

5. What is the final product in each reaction ?

(i) ?OHHC2I

NaOH52

(ii) ?CHClAg

heat3

(iii) ?CHCl3HNO

3

(iv) ?CCl OH/Fe4

2

(v) ?MgBrCH 3NH3

(vi) ?ClCH—CHCH KOH.Aq22

(vii) ?CHClCH KOH.Aq2

(viii) ?LiCH 22 CHCH3

(ix) ?CCl)CH( Zn)CH(33

23

(x) CH3

|

CH2 = C —CH

2CH

3 IBr

?

(xi) ?CHCHCH NBS23

(xii) ?BrCHCHCH HBr22

(xiii) CH3 — CH — CH — CH

3 ONaHC 52 ?

| | Br CH

3

6. What happens when ? Give equation only :

(i) Chlorine reacts with CS2 in presence of

anhydrous aluminium chloride.

(ii) Ethyl alcohol is heated with iodine andsodium hydroxide.

(iii) Ethyl alcohol reacts with bleachingpowder.

(iv) Chlorine is passes through ethyl alcohol.

(v) Ethyl bromide reacts with sodiumethoxide.

CAH – 16


New Delhi – 110 018, Ph. : 9312629035, 8527112111

(vi) Ethyl bromide reacts with silver cyanide.

(vii) Ethyl bromide is heated with zinc.

7. How will you obtain the following compounds fromethyl bromide ?

(a) Ethene, (b) n-Butane,

(c) Diethyl ether, (d) Ethyl acetate,

8. Describe the action of KOH (aq.) on :

(a) CH3Cl (b) CH

2Cl

2

(c) CHCl3

(d) CCl4

9. How will you synthesise :

(a) Isopropyl bromide from n-propylbromide.

(b) n-Propyl bromide from isopropylbromide.

(c) Propionic acid from ethyl bromide.

(d) Ethylene glycol from ethyl chloride.

(e) Vinyl bromide from ethyl alcohol

(f) Allyl chloride from propane

10. Complete the following by providing (A), (B), (C)and (D)

(i) )A(OHCHCHCH 3PBr223

)D()C()B( 3NHHBrKOH.Alc

(ii)

()A(ICHCHCH OH/HKOH.Alc223

2

)D()C()B(H

LiAlH

SOCl

4

2

(iii)

()A(CHBrCHCHHBr

Peroxide

KOH.Alc33

)D()C()B(Mg

Ether

NaI

Acetone

(iv) )A(CHCHCHCHNBS

Light223

)C()B( HBrKOH.Alc

11. How will you distinghish from the following :

(a) Chloroform and carbon tetrachloride.

(b) Ethyl chloride and vinyl chloride.

(c) Alkyl halide and an alkane.

(d) Ethylene bromide and ethylidenebromide

12. Identify the product (A), (B) and (C)

)C()B()A(HC2

32

I

CONaHydrolysisHBr42

13. Explain the following :

(a) Carbon tetrachloride is used as fireextinguisher.

(b) Alkyl iodides become darken onstanding in presence of light.

(c) A small amount of NaI or KI catalysesthe hydrolysis of RCl or the reaction,

RCl + R’ONa ROR’ + NaCl

(d) While preparing alkyl halides fromalkanes, dry gaseous hydro-halogenacids are used instead of their aqueoussolutions.

(e) Hydrogen atom of chloroform isdefinitely acidic in nature.

(f) Vinyl halide is less reactive while allylhalide is more reactive than alkyl halides.

(g) Why is free radical halogenation ofalkanes is seldom used for laboratorypreparation of alkyl halides ? Under whatcondition good yields ofmonosubstituted chlorides can beobtained ?

(h) What effect should the followingreasonance of vinyl chloride have on its

dipole moment ?

lCCHHClCHCCH 22

(i) 2-Chloro-3-methyl butane on treatmentwith alcoholic potash gives2-methylbutene-2 as the major product.

14. An halide C5H

11X on treating with alcoholic KOH

gives only pentene-1. What is halide ?

15. The alkyl halide C4H

9Cl (A) reacts with alcoholic

KOH and gives alkene (B) which reacts withbromine to form a dibromide (C). (C) istransformed with sodalime to a gas (D) which formsa precipitate with ammonical silver nitrate solution.Give the structures of (A), (B), (C) and (D). Explainthe reactions.

16. RCl is treated with Li in ether to form R — Li,R — Li reacts with water to form isopentane.R — Cl also reacts with sodium to form 2, 7-dim-ethyl octane. What is the structure of R — Cl ?

17. Which hydrocarbon is consistent with thefollowing formation ? Molecular mass = 72 gives asingle monochloride and two dichlorides onphotochlorination.

CAH – 17


New Delhi – 110 018, Ph. : 9312629035, 8527112111

18. With alcoholic potash C3H

7Br (A) gives C

3H

6 (B).

(B) on oxidation gives C2H

4O

2(C) + carbon dioxide

and water. With hydrobromic acid gives (D), anisomer of (A). Identify the compounds (A) to (D).

19. With alkali C3H

6Cl

2 (A) gives C

3H

6O (B) or C

3H

4

(C). (C) reacts with dilute H2SO

4 containing

mercuric sulphate to give C3H

6O (D) which gives

idoform test.

20. An organic compound (A) C7H

15Cl on treatment

with alcoholic caustic potash gives a hydrocarbon(B) C

7H

14. (B) on treatment with ozone and

subsequent hydrolysis gives acetone andbutyraldehyde. What are (A) and (B) ?

21. An alkyl halide (X) of formula C6H

13Cl on

treatment with potassium tertiary butoxide givestwo isomeric alkenes (Y) and (Z) of formula C

6H

12.

Both alkenes on hydrogenation give 2,3-dimethylbutane. Predict (X), (Y) and (Z).

FINAL STEP EXERCISE

(SUBJECTIVE)

1. Treatment of 2-bromobutane with hot alcoholicKOH gives a mixture of three isomeric butenes (A),(B) and (C). Ozonolysis of the minor product (A),gives formaldehyde and another aldehyde inequimolar amounts. Both (B) and (C) gave the samesingle product (D) on ozonolysis. What are the struc-tural formulae of (A), (B), (C) and (D) ?

2. A chloro compound (A) showed the followingproperties : (a) Decolourised bromine water, (b)Absorbed hydrogen catalytically, (c) givesprecipitate with ammonical cuprous chloride, (d)when vapourized 1.49 g of (A) gave 448 mL ofvapours at STP. Identify (A) and write down thereactions involved.

3. An organic compound (A), C5H

9Br which readily

decolourises bromine water and KMnO4 solution

gives (B), C5H

11Br on treatment with Sn/HCl. The

reaction of (A) with NaNH2 produces (C) with

evolution of ammonia. (C) neither reacts withsodium nor forms any metal acetylide but reactswith Lindlar catalyst to give (D) and on reactionwith Na/liq. NH

3 produces (E). Both the compounds

(D) and (E) are isomeric. Give structures of (A) to(E) with proper reasoning.

4. An organic compound (A), C4H

9Cl on reacting with

aqueous KOH gives (B) and on reaction withalcoholic KOH gives (C) which is also formed bypassing vapours of (B) over head copper. Thecompound (C) readily decolourises bromine water.Ozonolysis of (C) gives two compounds (D) and (E).Compound (D) reacts with NH

2OH to give (F) and

the compound (E) reacts with NaOH to give analcohol (G) and sodium salt (H) of an acid. (D) canalso be prepared from propyne on treatment withwater in presence of Hg2+ and H

2SO

4. Identify (A)

to (H) with proper reasoning.

5. Give the major product (with proper explanation)when following halogen compounds are treatedwith sodium ethoxide.

(a)

(b)

(c)

6. What are the products of the following reactions ?

(a)

(b)

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