Benzene Preparation and Physical Properties Class 11 Notes | EduRev

Chemistry for JEE

: Benzene Preparation and Physical Properties Class 11 Notes | EduRev

The document Benzene Preparation and Physical Properties Class 11 Notes | EduRev is a part of the Course Chemistry for JEE.

Benzene

The parent member of the family of aromatic hydrocarbons is benzene (molecular formula:C6H6). It has hexagonal ring of six carbon atoms with three double bonds at alternate positions. It is resonance stabilized and the structure may be represented as given below.

Benzene Preparation and Physical Properties Class 11 Notes | EduRev


Methods of Preparation:

(i) Cyclic polymerization of ethyne (See alkyne)

(ii) Decarboxylation of aromatic acids

(iii)  Benzene Preparation and Physical Properties Class 11 Notes | EduRev

Benzene Preparation and Physical Properties Class 11 Notes | EduRev


Physical Properties of Benzene:

  1. Aromatic hydrocarbons are non-polar molecules and are usually colourless liquids or solids with a characteristic aroma.
  2. Aromatic hydrocarbons are immiscible with water but readily miscible with organic solvents.
  3. Aromatic compounds burn with sooty flame.

Chemical Reactions of Benzene:

  1. Benzene gives electrophilic substitution reactions.
  2. According to experimental evidences, electrophilic substitution reaction involve following three steps:

(a) Generation of electrophilie
(b) Formation of carbocation intermediate.
(c) Removal of proton from the carbocation intermediate.

 

(i) Nitration

Benzene Preparation and Physical Properties Class 11 Notes | EduRev

 

(ii) Halogenation

Benzene Preparation and Physical Properties Class 11 Notes | EduRev

 

(iii) Sulphonation

Benzene Preparation and Physical Properties Class 11 Notes | EduRev

 

(iv) Friedel-Craft’s alkylation reaction

Benzene Preparation and Physical Properties Class 11 Notes | EduRev

When Friedel-Craft alkylation is carried out with CH3Cl, the product obtained is C6H5CH3. In case the alkylation is carried out with higher alkyl halide, e.g., n-propyl chloride, then the electrophile n-propyl carbocation (CH3 – CH2+CH2) which is a primary carbocation rearranges to form more stable secondary carbocation (iso-propyl carbocation), and the main product formed will be iso-propyl benzene.


(v) Friedel-Crafts acylation reaction

Benzene Preparation and Physical Properties Class 11 Notes | EduRev

(vi) With Cl2: In excess of chlorine, benzene yields hexachlorobenzene [C6Cl6].

Benzene Preparation and Physical Properties Class 11 Notes | EduRev

Benzene also undergoes addition reactions e.g.,

Benzene Preparation and Physical Properties Class 11 Notes | EduRev

Benzene Preparation and Physical Properties Class 11 Notes | EduRev


Combustion: 2C6H6 + 15O2 → 12CO2 + 6H2O


Reactions for Benzene:

Benzene Preparation and Physical Properties Class 11 Notes | EduRev  

 

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