Halogens Funcational Group


 
 
Concept Explanation
 

Halogens Funcational Group

Halogen derivatives of alkanes, alkenes and alkynes are known as alkyl halides (haloalkenes), alkenyl halides (haloalkanes) alkynyl halides (haloalkynes) respectively.

Besides the nature and number of halogen atoms, alkyl halides may be classified into primary (1^o), secondary (2^o) and tertiary (3^o) according to the nature of the carbon atom bearing halogen.

                                               CH_3CH_2CI, ; ; ; ; ; (CH_3)_2CHCl, ; ; ; ; ; ; (CH_3)_3CCl

                                               ethyl chloride (1^o)     Isopropyl chloride (2^o)       tert. Butyl chloride (3^o)

                                                                                (-CI ; on ; 2^oC)                 (-CI; on ; 3^oC)

Methods of Preparation

(i)   From alcohols with  

HX,PX_3(X=1, Br,CI); ; or ; ; SOCI_2

R-OH+HXrightarrow RX+H_2O

R-OH+PCI_5rightarrow R-CI+POCI_3+HCI

(ii) Addition of hydrogen halides to alkenes.          

    CH_2=CH_2+HBr rightarrow CH_3-CH_2Br

(iii)  From alkanes                                         

  R-H+X_2 overset{Delta ; or ; hv}{rightarrow} R-X+HX(X=CI,Br; or ; 1)

(iv)  From ethers                                      

       R-O-R+2HX overset{373 ; K}{rightarrow}2R-X+H_2O(X=Br ; or ; 1)

Physical Properties

(i)  Solubility: Alkyl halides are insoluble in water.

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Sample Questions
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Question : 1

Halogen derivatives of alkynes are known as ________________________.

Right Option : C
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Question : 2

Which of the following are correct :

(a) Boiling point decreases as the size of alkyl group decreases

(b) Stability decreases as the strength of C - X bond decreases.

(c) Alkyl halides are insolube in water.

Right Option : D
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Explanation
Question : 3

Halogen derivatives of alkanes are known as ________________________.

Right Option : B
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Explanation
 
 


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