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# Haloalkanes and Haloarenes

#### Multiple Choice Questions

1.

Assertion : Benzyl bromide when kept in acetone water it produces benzyl alcohol.

Reason : The reaction follows SN2 mechanism.

• If both assertion and reason are true and the reason is the correct explanation of the assertion.

• If both assertion and reason are true and the reason is not the correct explanation of the assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

A.

If both assertion and reason are true and the reason is the correct explanation of the assertion.

When benzyl bromide is kept in acetone, it produces benzyl alcohol.

2.

An asymmetric carbon atom is which

• attached three atoms or groups are different

• attached all the atoms or groups are different

• attached two atoms or groups are different

• attached all the atoms or groups are the same

B.

attached all the atoms or groups are different

An asymmetric carbon atomis defined as acarbonwithin an organic compound that contains four differentatomsor groups ofatoms(substituents) bonded to it.

3.

Which of the following possess highest melting point?

• p-dichlorobenzene

• m-dichlorobenzene

• o-dichlorobenzene

• chlorobenzene

A.

p-dichlorobenzene

p-dichlorobenzene moleculehas symmetrical structure. It can fit well in its crystal lattice. The intermolecular forces of attraction are strong. Hence, it possesses highest melting point among given options.

4.

Which ofthe following is involved in Sandmeyer'sreaction ?

• Ferrous salt

• Diazonium salt

• Ammonium salt

• Cupromonium salt

B.

Diazonium salt

Aryl halides can be prepared by thedecomposition of aryl diazonium salts in presence ofcopper halides solution dissolved in the correspondinghalogen acid, the diazo group is replaced by a halogenatom. This reaction is known as Sandmeyer reaction.

5.

CH3-CH2-Cl$\stackrel{\mathrm{alc}.\mathrm{KOH}}{\to }$A, the product is :

• CH3CH2OK

• CH3CHO

• CH3CH2OCH2CH3

• CH2=CH2

D.

CH2=CH2

Alkyl halides undergoes$\mathrm{\beta }$ - elimination in presence of alcoholic KOH, to give unsaturated hydrocarbons. This is also called dehydrodehalogenation of alkyl halides.

CH3.CH2Cl$\stackrel{\mathrm{alc}.\mathrm{KOH}}{\to }$$\underset{\mathrm{ethylene}}{{\mathrm{CH}}_{2}={\mathrm{CH}}_{2}}$+ KCl + H2O

6.

The reaction :

C2H5OH$\to$SOCl2$\stackrel{\mathrm{Pyridine}}{\to }$C2H5Cl + SO2 + HClis known as :

• Kharasch effect

• Williamson's synthesis

• Darzen's procedure

• Hunsdiecker reaction

C.

Darzen's procedure

Darzen's method : Alkyl halides are preparedwhen thionyl chloride and alcohols are refulxed inpresence of pyridine.

R-OH + SOCl2$\underset{\mathrm{reflux}}{\overset{\mathrm{Py}}{\to }}$R-Cl + SO2 + HCl

By products of this reaction are gases (SO2 , HCl) socan be easily removed from the reaction mixture.

7.

Assertion : Hydroxyketones are not directly used in Grignard reaction.

Reason : Grignard reagents react with hydroxyl group.

• If both assertion and reason are true and the reason is the correct explanation of the assertion.

• If both assertion and reason are true and the reason is not the correct explanation of the assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

A.

If both assertion and reason are true and the reason is the correct explanation of the assertion.

Hydroxyketones are not directly used in Grignard reaction as these are very reactive and will react with hydroxyl group.

8.

Chloroform , when kept open , is oxidisedto :

• CO2

• COCl2

• CO2 , Cl2

• none of these

B.

COCl2

Chloroform is oxidised to a poisonousgas , phosgene (COCl2)by atmosphericgas .

CHCl3 + O$\to$COCl2 + HCl

9.

Which of the following compounds reacts slower than benzene in electrophilic brornination?

A.

Nitro group (-NO2) deactivates the benzene ring in nitrobenzene due to -M effect.

10.

Assertion : Trans-2-butene on reaction with Br2 gives meso-2,3-dibromobutane.

Reason : The reaction involves syn -addition of bromine.

• If both assertion and reason are true and the reason is the correct explanation of the assertion.

• If both assertion and reason are true and the reason is not the correct explanation of the assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

C.

If assertion is true but reason is false.

With trans-2-butene, the product of Br2 addition is optically inactive due to the formation ofsymmetric mesa compounds.