NCERT Solutions Alkyl & Aryl Halides

In this course, we will discuss NCERT exercise solutions of our organic chemistry chapter of class 12 (XII), Alkyl and aryl halides also known as halogenated compounds. We will discuss each and every question in detail and I will provide you some super tricks to solve some of these questions.

We will be discussing following questions one by one

10.1    Name  the  following  halides  according  to  IUPAC  system  and  classify  them  as alkyl,  allyl,  benzyl  (primary,  secondary,  tertiary),  vinyl  or  aryl  halides:

(i)  (CH3)2CHCH(Cl)CH3                 (ii)  CH3CH2CH(CH3)CH(C2H5)Cl

(iii)  CH3CH2C(CH3)2CH2I                 (iv)  (CH3)3CCH2CH(Br)C6H5

(v)  CH3CH(CH3)CH(Br)CH3           (vi)  CH3C(C2H5)2CH2Br

(vii)  CH3C(Cl)(C2H5)CH2CH3          (viii)  CH3CH=C(Cl)CH2CH(CH3)2

(ix)  CH3CH=CHC(Br)(CH3)2             (x)  p-ClC6H4CH2CH(CH3)2

(xi)  m-ClCH2C6H4CH2C(CH3)3        (xii)  o-Br-C6H4CH(CH3)CH2CH3

10.2    Give  the  IUPAC  names  of  the  following  compounds:

(i)  CH3CH(Cl)CH(Br)CH3   (ii)  CHF2CBrClF   (iii)  ClCH2C≡CCH2Br

(iv)  (CCl3)3CCl   (v)  CH3C(p-ClC6H4)2CH(Br)CH3   (vi)  (CH3)3CCH=ClC6H4I-p

10.3    Write  the  structures  of  the  following  organic  halogen  compounds. (i)  2-Chloro-3-methylpentane                 (ii)  p-Bromochlorobenzene

(iii)  1-Chloro-4-ethylcyclohexane             (iv)  2-(2-Chlorophenyl)-1-iodooctane

(v)  Perfluorobenzene                               (vi) 4-tert-Butyl-3-iodoheptane

(vii)  1-Bromo-4-sec-butyl-2-methylbenzene   (viii)  1,4-Dibromobut-2-ene

10.4  Which  one  of  the  following  has  the  highest  dipole  moment?

(i)  CH2Cl2   (ii)  CHCl3   (iii)  CCl4

10.5  A  hydrocarbon  C5H10  does  not  react  with  chlorine  in  dark  but  gives  a  single monochloro  compound  C5H9Cl  in  bright  sunlight.  Identify  the  hydrocarbon.

10.6  Write  the  isomers  of  the  compound  having  formula  C4H9Br.

10.7  Write  the  equations  for  the  preparation  of  1-iodobutane  from

(i)  1-butanol   (ii)  1-chlorobutane   (iii)  but-1-ene.

10.8  What  are  ambident  nucleophiles?  Explain  with  an  example.

10.9  Which  compound  in  each  of  the  following  pairs  will  react  faster  in  SN2  reaction

with  –OH?   (i)  CH3Br  or  CH3I   (ii)  (CH3)3CCl  or  CH3Cl

10.10  Predict  all  the  alkenes  that  would  be  formed  by  dehydrohalogenation  of  the following halides with sodium ethoxide in ethanol and identify the major alkene:

(i)  1-Bromo-1-methylcyclohexane   (ii)  2-Chloro-2-methylbutane

(iii)  2,2,3-Trimethyl-3-bromopentane.

10.11  How  will  you  bring  about  the  following  conversions?

(i)  Ethanol  to  but-1-yne   (ii)  Ethane  to  bromoethene   (iii)  Propene  to

1-nitropropane   (iv)  Toluene  to  benzyl  alcohol   (v)  Propene  to  propyne (vi)  Ethanol  to  ethyl  fluoride   (vii)  Bromomethane  to  propanone   (viii)  But-1-ene to  but-2-ene   (ix)  1-Chlorobutane  to  n-octane   (x)  Benzene  to  biphenyl.

10.12  Explain  why

(i)  the dipole moment of chlorobenzene is lower than that of cyclohexyl chloride?

(ii)  alkyl  halides,  though  polar,  are  immiscible  with  water?

(iii)  Grignard  reagents  should  be  prepared  under  anhydrous  conditions?

10.13  Give  the  uses  of  freon  12,  DDT,  carbon  tetrachloride  and  iodoform.

10.14  Write the structure of the major organic product in each of the following reactions:

(i)  CH3CH2CH2Cl  +  NaI

(ii)  (CH3)3CBr    +    KOH

(iii)  CH3CH(Br)CH2CH3    +    NaOH

(iv)  CH3CH2Br    +    KCN

(v)  C6H5ONa    +    C2H5Cl

(vi)  CH3CH2CH2OH    +  SOCl2

(vii)  CH3CH2CH  =  CH2  +    HBr (viii)  CH3CH  =  C(CH3)2    +    HBr

10.15  Write  the  mechanism  of  the  following  reaction:

nBuBr    +    KCN                           nBuCN

10.16  Arrange  the  compounds  of  each  set  in  order  of  reactivity  towards  SN2 displacement:

(i)  2-Bromo-2-methylbutane,  1-Bromopentane,  2-Bromopentane

(ii)  1-Bromo-3-methylbutane, 2-Bromo-2-methylbutane, 3-Bromo-2-methylbutane

(iii)  1-Bromobutane,  1-Bromo-2,2-dimethylpropane,  1-Bromo-2-methylbutane, 1-Bromo-3-methylbutane.

10.17  Out of C6H5CH2Cl and C6H5CHClC6H5, which is more easily hydrolysed by aqueous KOH?

10.18  p-Dichlorobenzene has higher m.p. and solubility than those of o- and m-isomers. Discuss.

10.19  How  the  following  conversions  can  be  carried  out?

(i)  Propene  to  propan-1-ol

(ii)  Ethanol  to  but-1-yne

(iii)  1-Bromopropane  to  2-bromopropane

(iv)  Toluene  to  benzyl  alcohol

(v)  Benzene  to  4-bromonitrobenzene

(vi)  Benzyl  alcohol  to  2-phenylethanoic  acid

(vii)  Ethanol  to  propanenitrile

(viii)  Aniline  to  chlorobenzene

(ix)  2-Chlorobutane  to  3,  4-dimethylhexane

(x)  2-Methyl-1-propene  to  2-chloro-2-methylpropane

(xi)  Ethyl  chloride  to  propanoic  acid

(xii)  But-1-ene  to  n-butyliodide

(xiii)  2-Chloropropane  to  1-propanol

(xiv)  Isopropyl  alcohol  to  iodoform

(xv)  Chlorobenzene  to  p-nitrophenol

(xvi)  2-Bromopropane  to  1-bromopropane

(xvii)  Chloroethane  to  butane

(xviii)  Benzene  to  diphenyl

(xix)  tert-Butyl  bromide  to  isobutyl  bromide

(xx)  Aniline  to  phenylisocyanide

10.20  The  treatment  of  alkyl  chlorides  with  aqueous  KOH  leads  to  the  formation  of alcohols but in the presence of alcoholic KOH, alkenes are major products. Explain.

10.21  Primary alkyl halide C4H9Br (a) reacted with alcoholic KOH to give compound (b).

Compound  (b)  is  reacted  with  HBr  to  give  (c)  which  is  an  isomer  of  (a).  When (a) is reacted with sodium metal it gives compound (d), C8H18 which is different

from  the  compound  formed  when  n-butyl  bromide  is  reacted  with  sodium. Give the structural formula of (a) and write the equations for all the reactions.

10.22  What  happens  when

(i)  n-butyl  chloride  is  treated  with  alcoholic  KOH,

(ii)  bromobenzene  is  treated  with  Mg  in  the  presence  of  dry  ether,

(iii)  chlorobenzene  is  subjected  to  hydrolysis,

(iv)  ethyl  chloride  is  treated  with  aqueous  KOH,

(v)  methyl  bromide  is  treated  with  sodium  in  the  presence  of  dry  ether,

(vi)  methyl  chloride  is  treated  with  KCN?