Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

Class 12 Chemistry 35 Years JEE Mains &Advance Past yr Paper

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1. (a) Show by chemical equations only, how you would prepare the following from the indicated starting materials. Specify the reagents in each step of the
 synthesis.
 (i) Hexachlorethane, C2Cl6, from calcium carbide.
 (ii) Chloroform from carbon disulphide.
 (b) Give one chemical test which would distinguish between C2H5OH from CHCl3.           (1979)

 Solution : 

(a)

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev
(b) Carbylamine test.
CHCl3 + aq KOH + aniline (i.e. primary amine) → bad smelling isocyanide
C2H5OH + aq KOH + aniline → No reaction

 

2. Write the structural formula of the major product in each of the following cases :
 (i) chloroform reacts with aniline in the presence of excess alkali                (1981 - ½ Mark)
 (ii) bromoethane reacts with one-half of the molar quantity
 of silver carbonate.           (1981 - ½ Mark)

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

 

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

 

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

 

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

Solution : 

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev carbocations are formed on addition of HBr on C6H5CH=CHCH3, the latter being benzylic carbocation,
is stabilised due to resonance and hence Br adds on it forming C6H5CHBr.CH2CH3 as the final product.]
 

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

 

 

3. Give reasons for the following :
 (i) 7-Bromo-1, 3, 5-cycloheptatriene exists as ionic compound, while 5-bromo-1, 3-cyclopentadiene does not ionise even in presence of Ag+ ion. Explain.
 (2004 - 2 Marks)

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev  Neutral solution. Explain.                                                     (2005 - 1 Mark)

Solution : 

(i) TIPS/Formulae :
7-Bromo-1,3,5-cycloheptatriene is aromatic whereas
5-Bromo-1,3-Cycloheptadiene is non aromatic.

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

(ii) NOTE : The former halide is a 3° halide, hence it undergoes SN1 reaction forming HBr, as one of the products, which make solution acidic

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev is an aryl halide so it does not undergo nucleophilic substitution reactions. Hence the solution will remain neutral.

 

4. State the conditions under which the following preparation are carried out. Give the necessary equations which need not be balanced :
 (i) Lead tetraethyl from sodium-lead alloy  (1983 - 1 Mark)
 (ii) Methyl chloride from aluminium carbide   (1983 - 1 Mark)
 solution : 

(i) 4C2H5Br + 4(Na–Pb)   Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev  Pb(C2H5)4 + 4NaBr + 3Pb
Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

 

5. Write the structure of all the possible isomers of dichloroethene. Which of them will have zero dipole moment?     (1985 - 2 Marks)
 Solution : 

Dichloroethene exists in three isomeric forms.

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

 

6. What happens when excess chlorine is passed through boiling toluene in the presence of sunlight?(1987 - 1 Mark)
 Solution : 

 

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev
NOTE : This follows free radical mechanism.]

 

7. What effect should the following resonance of vinyl chloride have on its dipole moment? (1987 - 1 Mark)

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

Solution : 
 TIPS/Formulae :

Resonance decreases the dipole moment of vinyl chloride (CH2 = CHCl). The positive charge on Cl and a negative charge on C (developed by resonance) oppose each other and hence diminish the electronegativity of Cl and thus polarity (and dipole moment) of the bond. The dipole moments of vinyl chloride and chlorobenzene are 1.4D and 1.7D respectively, while the dipole moment of alkyl halides is 2–2.2D.

 

8. An organic compound X, on analysis gives 24.24 per cent carbon and 4.04 per cent hydrogen. Further, sodium extract of 1.0 g of X gives 2.90 g of silver chloride with acidified silver nitrate solution. The compound X may be represented by two isomeric structures, Y and Z. Y on treatment with aqueous potassium hydroxide solution gives a dihydroxy compound while Z on similar treatment gives ethanal. Find out the molecular formula of X and give the structures of Y and Z. (1989 - 4 Marks)
Solution : 
Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev
Empirical formula of (X)
 

Element%Relative no. of atomsSimplest ratio
C24.242.021
H4.044.042
Cl71.722.021

 ∴ Empirical formula of (X) is CH2Cl
Since X has two isomers Y and Z; both react with KOH(aq).

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev dihydroxy compound i.e. 2Cl atoms on adjacent carbon

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev CH3CHO i.e. Z should have 2Cl atoms on one C atom
Thus Z should be CH3CHCl2 (1, 1-dichlorethane) and
Y should CH2ClCH2Cl (1, 2-dichloroethane)

Reactions :

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

 

 

9. Draw the stereochemical structures of the products in the following reaction : (1994 - 4 Marks)

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

Solution: 

 SN2 reaction leads to inversion in configuration
Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

 

10. An alkyl halide, X, of formula C6H13Cl on treatment with potassium tertiary butoxide gives two isomeric alkenes Y and Z (C6H12). Both alkenes on hydrogenation give 2, 3-dimethylbutane. Predict the structures of X, Y and Z.                (1996 - 3 Marks)

Solution : 
Summary of the given facts
 

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev
The two isomeric precursors of  (Y and Z) of 2, 3-dimethylbutane

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

Hence the precursor of Y & Z should  have following structure which explains all the given facts

 

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

 

 

11. How will you prepare m-bromoiodobenzene from benzene (in not more than 5-7 steps)?         (1996 - 2 Marks)
 Solution : 

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

 

12. Cyclobutyl bromide on treatment with magnesium in dry ether forms an organometallic (A). The organometallic reacts with ethanal to give an alcohol (B) after mild acidification. Prolonged treatment of alcohol (B) with an equivalent amount of HBr gives 1–bromo–1–methylcyclopentane (C). Write the structures of (A), (B) and explain how (C) is obtained from (B).             (2001 - 5 Marks)

Solution : 
 

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev
 

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev

 

Subjective questions of Haloalkanes and Haloarenes, Past year Questions - JEE Advance, Class 12 JEE Notes | EduRev 

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