Halogen Derivatives : Daily Practice Problems (DPP) - 2 | Additional Study Material for NEET PDF Download

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DPP : 01 / Halogen Derivatives
HALOGEN DERIVATIVES
DAILY  PRACTICE  PROBLEMS - 1
Topics covered under
AIPMT : Haloalkanes: Nomenclature, nature of C –X bond, physical and chemical properties, mechanism of substitution
reactions. Optical rotation. Haloarenes: Nature of C-X bond, substitution reactions (directive influence of halogen
for monosubstituted compounds only). Uses and environment effects of – dichloromethane, trichloromethane,
tetrachloromethane, iodoform, freons, DDT.
JEE-Mains cum Advance : Alkyl Halides: rearrangement reactions of alkyl carbocation, Grignard reactions, nucleophilic
substitution reactions,  Haloarenes : nucleophilic aromatic substitution in haloarenes and substituted haloarenes
(excluding Benzyme mechanism and cine substitution). Nature of C—X bond, mechanisms of substitution reactions,
uses, environmental effects of chlororform, iodoform, freons and DDT.
Some important points & facts
PREPARATION OF ALKYL HALIDES
I. From Alcohols
ROH
Alcohol
HCl(g) + Anhyd. ZnCl
2
HBr(48%) + conc.H
2
SO
4
(little),Reflux
or KBr + conc.H
2
SO
4
,Reflux
HI(57%), Reflux or KI + H
3
PO
4
,Reflux
PCl
5
PX
3
(or P + X
2
) SOCl
2
/Pyridine
R—Cl + H
2
O(Grove' s process) R—Br + H
2
O
R—I + H
2
O
R—Cl +POCl
3
+ HCl
3 R—X + H
3
PO
3
(X = Cl, Br or Cl) R—Cl + SO
2
+HCl(Darzen' s process) II. From Alkenes.
(a) Addition of halogen acids of alkenes gives alkyl halides. In absence of peroxides, addition to unsymmetrical
alkenes occurs according to Markovnikov’s rule while in presence of peroxides (ROOR), i.e., (C
6
H
5
COO) 2
,
H
2
O
2
, etc. the addition of only HBr (and not of HF, HCl or HI) occurs anti to Markovnikov’s rule. This is also
called peroxide effect or kharasch effect.
R—CH = CH
2
+ HBr
Absence of
Peroxides Peroxides
Presence of
R—CH
2
—CH
2
Br R—CHBr—CH
3
(Markvnikov' s
addn. product)(Anti-Markovnikov' s
addn. product) Pr esence or absence
3 2 3 3 of peroxides
Propene 2 Chloropropane
CH CH CH HC CH CHC CH
- - = + - - - - - - - ? - - l l
Page 2


SCF-07, 1
st
 floor,Sector-15, Panchkula
9217610408,8699438881,8699438882
Page No.1
without ability to achieve them.
God has never given dreams
DPP : 01 / Halogen Derivatives
HALOGEN DERIVATIVES
DAILY  PRACTICE  PROBLEMS - 1
Topics covered under
AIPMT : Haloalkanes: Nomenclature, nature of C –X bond, physical and chemical properties, mechanism of substitution
reactions. Optical rotation. Haloarenes: Nature of C-X bond, substitution reactions (directive influence of halogen
for monosubstituted compounds only). Uses and environment effects of – dichloromethane, trichloromethane,
tetrachloromethane, iodoform, freons, DDT.
JEE-Mains cum Advance : Alkyl Halides: rearrangement reactions of alkyl carbocation, Grignard reactions, nucleophilic
substitution reactions,  Haloarenes : nucleophilic aromatic substitution in haloarenes and substituted haloarenes
(excluding Benzyme mechanism and cine substitution). Nature of C—X bond, mechanisms of substitution reactions,
uses, environmental effects of chlororform, iodoform, freons and DDT.
Some important points & facts
PREPARATION OF ALKYL HALIDES
I. From Alcohols
ROH
Alcohol
HCl(g) + Anhyd. ZnCl
2
HBr(48%) + conc.H
2
SO
4
(little),Reflux
or KBr + conc.H
2
SO
4
,Reflux
HI(57%), Reflux or KI + H
3
PO
4
,Reflux
PCl
5
PX
3
(or P + X
2
) SOCl
2
/Pyridine
R—Cl + H
2
O(Grove' s process) R—Br + H
2
O
R—I + H
2
O
R—Cl +POCl
3
+ HCl
3 R—X + H
3
PO
3
(X = Cl, Br or Cl) R—Cl + SO
2
+HCl(Darzen' s process) II. From Alkenes.
(a) Addition of halogen acids of alkenes gives alkyl halides. In absence of peroxides, addition to unsymmetrical
alkenes occurs according to Markovnikov’s rule while in presence of peroxides (ROOR), i.e., (C
6
H
5
COO) 2
,
H
2
O
2
, etc. the addition of only HBr (and not of HF, HCl or HI) occurs anti to Markovnikov’s rule. This is also
called peroxide effect or kharasch effect.
R—CH = CH
2
+ HBr
Absence of
Peroxides Peroxides
Presence of
R—CH
2
—CH
2
Br R—CHBr—CH
3
(Markvnikov' s
addn. product)(Anti-Markovnikov' s
addn. product) Pr esence or absence
3 2 3 3 of peroxides
Propene 2 Chloropropane
CH CH CH HC CH CHC CH
- - = + - - - - - - - ? - - l l
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DPP : 01 / Halogen Derivatives
(b) Allylic halogenation. The carbon atom next to the double bond is called allylic carbon and the hydrogens
attached to it are called allylic hydrogens. These hydrogens can be replaced by halogens (Cl or Br) by
heating at 775 K.
() 775K
3 2 2 2 2
3 Chloro 1 propene Propene
Allyl chloride
CH CH CH C C CH CH CH HC
- - - - = + - - -? - = + l l l
775K
3 2 2 2 2
3 Bromo 1 propene Propene
CH CH CH Br Br CH CH CH HBr
- - - - = + - - -? - - = +
475K,hv
3 2 2 2 2 2 2 traces of peroxides
Allyl chloride Propene
CH CH CH SO C C CH CH CH SO HC - = + - - - - - - - ? - - = + + l l l
3 2
Propene
CH CH CH - = +
hv
2 2 Benzoyl Peroxide
Allyl bromide
Br CH CH CH - - - - - -? - - = +
CH
2
—CO
CH
2
—CO
NBr
NBS
Succinimide
CH
2
—CO
CH
2
—CO
NH
III. From Alkanes
() I
or hv
2
R H X R X HX X C ,Br or
?
- + - - - - ? - + = l
IV. By Halogen Exchange Method
I I
Acetone or Methanol
R C Na R NaC - + - - - - - - -? - + l l
This reaction is called Finkelstein reaction.
V. Borodine-Hunsdlecker Reaction. The silver salt of carboxylic acids on reaction with Br
2
 in refluxing CCl
4
 undergo
decarboxylation to form alkyl and aryl bromides with one carbon atom less than the original acid used.
4
CCl / Re flux
3 2 3 2
Silver acetate Methyl bromide
CH COOAg Br CH Br AgBr CO + - - - - -? - + +
4
CCl /Re flux
6 5 2 6 5 2
Silver benzoate Bromobenzene
C H COOAg Br C H Br AgBr CO + - - - - -? + +
Objective Questions
1. Which one is incorrect ?
(a) o and p directing influence of halogens is due to their +R effect
(b) +R effect of Cl is stronger than that of F
(c) Halogens show –I effect and so are deactivating
(d) Cl is more deactivating than I
2. Whenever inductive effect and resonance effect operate together then
(a) resonance effect overweighs Inductive effect
(b) inductive effect overweighs resonance effect
(c) both are equal
(d) there is no connection between resonance and inductive effect
3. Which of the following is correct for stability of phenoxide ion ?
(a) resonating structure of benzene ring(b) localization of p-electron in phenoxide ion
(c) delocalization of p-electron in phenoxide ion(d) all of the above