Haloalkanes and Haloarenes Test

Result

Haloalkanes and Haloarenes Test - 19

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Weekly Quiz Competition

Question 1
1 / -0

Molecules whose mirror image is non-superimposable over them are known as chiral. Which of the following molecules is chiral in nature?

A
2-Bromobutane

B
1-Bromobutane

C
2-Bromopropane

D
2-Bromopropan-2-ol

Solution

The objects which are non -superimposable on their mirror images are called enantiomers. It occurs on that molecule which contains asymmetric carbon or chiral ( i.e., a carbon atom attached with four different groups.) in the present case a molecule of 2- Bromobutane [ \(CH_3 CH_2 C^\ast H (Br) CH_3\) ] is a chiral molecule because,

(i) It contains a chiral carbon atom marked as (C*).

(ii) Its mirror image is non-superimposable over them.
Question 2
1 / -0

Which of the following compounds will give racemic mixture on nucleophilic substitution by \(OH^-\) ion?

(a) \(CH_3 -\underset{\underset{C_2H_5}{|}}{CH}-Br\)

(b) \(CH_3- \underset{ \overset{|}{C_2H_5}}{\stackrel{\overset{Br}{|}}{C}} - CH_3\)

(c) \(CH_3 -\underset{\underset{C_2H_5}{|}}{CH}-CH_2Br\)

A
(a)

B
(a), (b), (c)

C
(b), (c)

D
(a), (c)

Solution

A mixture containing two enantiomers in equal proportions will have zero optical rotation, as the rotation due to one isomer will be cancelled by the rotation due to the other isomer. Such a mixture is known as racemic mixture or racemic modification. A racemic mixture is represented by prefixing (dl) in case of optically active alkyl halides, \(S_N1\) reactions are accompanied by racemisation. In the present case,

*both the compounds are optically active due to presence of chiral carbon atoms,

* both of them would undergo SNI reaction,

Hence ,they would exhibit racemisation to give a racemic mixture.
Question 3
1 / -0

Which is the correct increasing order of boiling points of the following compounds?

1-Iodobutane, 1-Bromobutane, 1-Chlorobutane, Butane

A
Butane < 1-Chlorobutane < 1-Bromobutane < 1-Iodobutane

B
1-Iodobutane < 1-Bromobutane < 1-Chlorobutane < Butane

C
Butane < 1-Iodobutane < 1-Bromobutane < 1-Chlorobutane

D
Butane < 1-Chlorobutane < 1-Iodobutane < 1-Bromobutane

Solution

For the same alkyl group, the boiling points of alkyl halides decrease in the order: RI > RBr > RCl > RF. This is because with the increase in size and mass of halogen atom, the magnitude of van der Waal forces increases.