Organic chemistry practice questions part 2

Haloalkanes and Haloarenes
Multiple Choice Questions (Type-I)

1. The order of reactivity of following alcohols with halogen acids is ___________.
(A) CH3CH2 —CH2—OH




(i) (A) > (B) > (C)
(ii) (C) > (B) > (A)
(iii) (B) > (A) > (C)
(iv) (A) > (C) > (B)
Ans. (ii)
Explanation: Greater the stability of carbocation, greater will be its ease of formation
from alkyl halide and faster will be the rate of reaction. In case of alkyl halides, 30 alkyl
halides undergo SNI reaction very fast because of the high stability of 30 carbocations.

2. Which of the following alcohols will yield the corresponding alkyl chloride on
reaction with concentrated HCl at room temperature?
(i) CH3CH2—CH2 —OH




Ans. (iv)
Explanation: The reactions of primary and secondary alcohols with HCl require the
presence of a catalyst, ZnCl2. With tertiary alcohols, the reaction is conducted by simply
shaking with concentrated HCl at room temperature. The order of reactivity of alcohols
with a given haloacid is 3o>2o>1o.

3. Identify the compound Y in the following reaction.

,Ans. (i)
Explanation: The Cl-, Br- and CN- nucleophiles can easily be introduced in the benzene
ring of diazonium salts in the presence of Cu(I) ion.

CuCl / HCl
→ ArCl + N 2
+ −
Ar N 2 X 
CuBr / HBr
→ ArBr + N 2
→
CuCN / KCN
ArCN + N 2

4. Toluene reacts with a halogen in the presence of iron (III) chloride giving ortho and
para halo compounds. The reaction is
(i) Electrophilic elimination reaction
(ii) Electrophilic substitution reaction
(iii) Free radical addition reaction
(iv) Nucleophilic substitution reaction
Ans. (ii)
Explanation: Aryl Chlorides and bromides can be easily prepared by electrophilic
substitution of arenes with chlorine and bromine respectively in the presence of Lewis
acid catalysts like iron or iorn (III) chloride.

5. Which of the following is halogen exchange reaction?
(i) RX + NaI → RI + NaX



(iii) R − OH + HX 
ZnCl2
→ R − X + H 2O

,Ans. (i)
Explanation: Alkyl iodides are often prepared by the reaction of alkyl
chlorides/bromides with Nal in dry acetone. This reaction is known as Finkelstein
reaction.
NaCl or NaBr thus formed is precipitated in dry acetone. It facilitates the forward reaction
according to Le Chatelier’s Principle.

6. Which reagent will you use for the following reaction?
CH3CH2CH2CH3 → CH3CH2CH2CH2Cl + CH3CH2CHClCH3
(i) Cl2/UV light
(ii) NaCl + H2SO4
(iii) Cl2 gas in dark
(iv) Cl2 gas in the presence of iron in dark
Ans. (i)
Explanation: Free radical chlorination or bromination of alkanes gives a complex
mixture of isomeric mono- and polyhaloalkanes, which is difficult to separate as pure
compounds. Consequently, the yield of any one free radical chlorination or bromination
of alkanes gives a complex
CH3CH 2 CH 2 CH 3 →
Cl2 /UV light
or heat
CH3CH 2 CH 2 CH 2 Cl + CH 3CH 2 CHClCH3

7. Arrange the following compounds in the increasing order of their densities.

, (i) (a) < (b) < (c) < (d)
(ii) (a) < (c) < (d) < (b)
(iii) (d) < (c) < (b) < (a)
(iv) (b) < (d) < (c) < (a)
Ans. (i)
Explanation: Density is related to molecular mass. Higher the mass, higher will be the
density of the molecule.

8. Arrange the following compounds in increasing order of their boiling points.



(b) CH3CH2CH2CH2Br




(i) (b) < (a) < (c)
(ii) (a) < (b) < (c)
(iii) (c) < (a) < (b)
(iv) (c) < (b) < (a)
Ans. (iii)
Explanation: As the branching increases, surface area of the molecule decreases. Because
of these the vander Waals force of attraction between the molecule decreases and
consequently boiling point decreases.

9. In which of the following molecules carbon atom marked with asterisk (*) is
asymmetric?