Haloalkanes and Haloarenes Test

Result

Haloalkanes and Haloarenes Test - 7

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Weekly Quiz Competition

Question 1
1 / -0

Alkyl halides are insoluble in water

A
weak hydrogen bonds exist between water molecules

B
high energy is released when newattractions are set up between the haloalkane and the water molecules

C
he force of attraction between the alkyl halide and water is weaker and cannot overcome the force of attraction between alkyl halide and alkyl halide as also that of water and water molecules

D
alkyl halides are non polar compounds

Solution

In alkyl halides, there exist dipole-dipole attractions where as in water van der waal's forces or the hydrogen bonding exists.. It is difficult for alkyl halides to break these hydrogen bonds, hence making them almost insoluble in water.
Question 2
1 / -0

Hydrocarbons are prepared from Grignard reagent by

A
by reacting them with sodium

B
by exposing them to Magnesium

C
by exposing them to diethyl ether

D
by reacting them with water

Solution

Grignard reagents are highly reactive and react with any source of proton to give hydrocarbons. Even water, alcohols, amines are sufficiently acidic to convert them to corresponding hydrocarbons. Thus Grignard reagent abstracts acidic hydrogen from H₂O forming alkane.

RMgX + H₂O → RH + Mg(OH)X
Question 3
1 / -0

Grignard reagent should be prepared under anhydrous conditions because

A
it can react with any source of protons to give hydrocarbons

B
the Mg – halogen bond is essentially ionic

C
the carbon – Mg bond is covalent but highly polar

D
All of these

Solution

In the Grignard reagent, the carbon-magnesium bond is covalent but highly polar, with carbon pulling electrons from electropositive magnesium; the magnesium halogen bond is essentially ionic.
Grignard reagents are highly reactive and react with any source of proton to give hydrocarbons. Even water, alcohols, amines are sufficiently acidic to convert them to corresponding hydrocarbons.

RMgX + H₂O → RH + Mg(OH)X
It is therefore necessary to avoid even traces of moisture from a Grignard reagent.
Question 4
1 / -0

Hydrocarbons having double the number of carbon atoms than present in the original alkyl halide are produced by using

A
Wurtz reaction

B
Sandmeyer’ reaction

C
Williamson’s synthesis

D
Fittig reaction

Solution

The Wurtz reaction, named after Charles-Adolphe Wurtz, is a coupling reaction in organic chemistry, organometallic chemistry and recently inorganic main group polymers, whereby two alkyl halides are reacted with sodium metal in dry ethereal solution to form a higher alkane:
2R - X + 2Na → R - R + 2NaX
Question 5
1 / -0

To prepare alkanes containing odd number of carbon atoms, Wurtz reaction is not preferred because

A
a mixture of two different alkyl halides has to be used

B
a lot of reaction mixture goes wasted

C
a mixture of four different alkyl halides has to be used

D
a mixture of three different alkyl halides has to be used

Solution

Alkyl halides on treatment with sodium metal in dry ethereal (free from moisture) solution give higher alkanes. This reaction is known as Wurtz reaction and is used for the preparation of higher alkanes containing even number of carbon atoms. Many side products are formed when two different alkyl halides are used. So this method is not preferred to prepare alkanes having odd number of C atoms.