Haloalkanes and Haloarenes Test

Result

Haloalkanes and Haloarenes Test - 18

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Weekly Quiz Competition

Question 1
1 / -0

Which of the following compounds are gem-dihalides?

(i) Ethylidene chloride

(ii) Ethylene dichloride

(iii) Methylene chloride

(iv) Benzyl chloride

A
(ii) and (iii)

B
(ii) and (iv)

C
(i) and (iii)

D
(i) and (ii)

Solution

gem - dihalides contain two halogen atoms bonded with the same carbon atom in their chain structures as shown below

\(H_3C - CHCl_2 \) and methylene chloride \(CH_2Cl_2.\)

Ethylidene chloride (gem -dihalide)

This condition is fulfilled by both the compounds at (i) & (iii)
Question 2
1 / -0

Assertion : tert-Butyl bromide undergoes Wurtz reaction to give 2, 2, 3, 3-tetramethyl butane.

Reason : In Wurtz reaction, alkyl halides react with sodium in dry ether to give hydrocarbon containing double the number of carbon atoms present in the halide.

A
Assertion and reason both are correct and reason is correct explanation of assertion.

B
Assertion and reason both are wrong statements.

C
Assertion is correct but reason is wrong statement.

D
Assertion is wrong but reason is correct statement.

Solution

Both the given statements for ' Assertion and Reason are correct and reason is correct explanation of assertion, because according to Wurtz reaction - itis" A reaction in which alkyl halides react with sodium in dry ether to give a hydrocarbon containing double the number of carbon atoms present in the halide." In this case, the product 2,2,3,3- tetramethyl butane contains double the number of carbon atoms as compared to tert- Butyl bromide.
Question 3
1 / -0

Assertion : Presence of a nitro group at ortho or para position increases the reactivity of haloarenes towards nucleophilic substitution.

Reason : Nitro group, being an electron-withdrawing group decreases the electron density over the benzene ring.

A
Assertion and reason both are correct and reason is correct explanation of assertion.

B
Assertion and reason both are wrong statements.

C
Assertion is correct but reason is wrong statement.

D
Assertion is wrong but reason is correct statement.

Solution

The presence of nitro group at ortho-and para-positions withdraws the electron density from the benzene ring and thus facilitates the attack of the nucleophile on haloarene. The carbanion thus formed is stabilised through resonance. The negative charge appeared at ortho- and para- positions with respect to the halogen substituent is stabilised by - \(NO_2\) group.

This confirms that both the given statements for assertion and reason are correct and reason is not correct explanation of assertion.

The correct statement for reason should be " The negative charge appeared at ortho and para positions with respect to halogen substituent is stabilised by \(NO_2\) group ".
Question 4
1 / -0

Assertion : In monohaloarenes, further electrophilic substitution occurs at ortho and para positions.

Reason : Halogen atom is a ring deactivator.

A
Assertion and reason both are correct and reason is correct explanation of assertion.

B
Assertion and reason both are wrong statements.

C
Assertion is correct but reason is wrong statement.

D
Assertion is wrong but reason is correct statement.

Solution

Halogen atom besides being slightly deactivating is o, p-directing; therefore, further substitution occurs at ortho-and para-positions with respect to the halogen atom. The o, p-directing influence of halogen atom can be easily understood by taking into account of the related resonating structures in haloarenes. Due to resonance, the electron density increases more at ortho and para positions than at meta position. Again, the halogen atom because of its -I effect has some tendency to withdraw electrons from the benzene ring, as a result, the ring gets some what deactivated as compared to benzene.
Question 5
1 / -0

Assertion : Aryl iodides can be prepared by reaction of arenes with iodine in the presence of an oxidising agent.

Reason: Oxidising agent oxidises \(I_2\) into HI.

A
Assertion and reason both are correct and reason is correct explanation of assertion.

B
Assertion and reason both are wrong statements.

C
Assertion is correct but reason is wrong statement.

D
Assertion is wrong but reason is correct statement.

Solution

(i) Directiodination of arene is possible to yield aryl iodide in presence of Lewis acids (viz. \(FeCl_3\) or \(AlCl_3\)) or even in presence of sunlight. Therefore, the statement' aryl iodides can be prepared by reaction with iodine in presence of an oxidising agent' is wrong.

(ii) However, aryl iodides are not obtained directly from arenes by using( oxidising agents + \(I_2\)) Actually, we need to convert arene to its diazonium salt, which when reacted with \(I_2\) yields aryl iodide.

(iii) Further, the statement (ie. ' Oxidising agent oxidises \(I_2\) to HI'), is also wrong because \(I_2\) on oxidation with an oxidising agent (viz. \(HNO_3\)) gives \(HIO_3\) (hydroiodic acid) as a product. So, the given for reason is wrong.