Structure of Benzene



STRUCTURE OF BENZENE
DISCUSSION
    HERE WE ARE GOING TO DISCUSS WHY BENZENE DOES NOT HAVE AN OPEN CHAIN STRUCTURE.     IN THE COMING LINES WE WILL COVER DIFFERENT POSSIBILITIES RELATED TO THE STRUCTURE     OF BENZENE MOLECULE.
    Structure of benzene is a controversial topic because benzene has outstanding characteristics. It     behaves both as saturated and unsaturated hydrocarbon. Here we discuss different aspects of the     structure of benzene.
LET US ASSUME THAT BENZENE BELONGS TO ALKANE FAMILY
    
    In case of an alkane, molecular formula of benzene must be the according to CnH2n+2 i.e. C6H14. but     there are only six H-atoms in benzene molecule. This shows that benzene does not belong to alkane     family.
LET US ASSUME THAT BENZENE BELONGS TO ALKENE FAMILY
    In case of an alkene, molecular formula of benzene must follow CnH2n i.e. C6H12. but there are six     H-atoms in benzene instead of 12. This shows that benzene is not a member of alkene family.
LET US ASSUME THAT BENZENE BELONGS TO ALKYNE FAMILY
    In case of alkyne, molecular formula of benzene must be according to CnH2n-2 i.e. C6H10. this shows     that for six C-atoms there must be 10 H-atoms and benzene contains only six H-atoms. This     concludes that benzene is not an alkyne.
LET BENZENE BELONGS TO OPEN CHAIN
HYDROCARBONS CONTAINING MULTIPLE BOND
    If we assume that benzene belongs to any hydrocarbon which contains multiple bonds then we can     draw some Possible structures of C6H6 molecule like the one:
CH2=CH-CH=C=C=CH2
    But this type of compound is a highly unsaturated compound and it must give addition reactions     under ordinary conditions.Now we discuss benzene in the light of reactions.
STRUCTURE OF BENZENE IN THE
LIGHT OF
CHEMICAL REACTIONS
    If we compare the reactions of benzene with the reactions of any aliphatic hydrocarbon (alkene or     alkyne) it must give the following type of reactions.
    C6H6 + X2 ® C6H6X2 + C6H6X4 + C6H6X6 (all are addition reactions)
    But in actual practice this reaction is not observed. However, benzene gives the following type of     reactions:
    C6H6 + X2 ®C6H5X + HX
    Which is a substitution reaction. This shows that benzene does not belong to aliphatic hydrocarbon     but it must be a special type of hydrocarbon.
    It should be noted down that benzene gives addition reactions but under extraordinary conditions like
    C6H6 + 3H® C6H12 (Cyclo Hexane)
    C6H6 + 3Cl2 ® C6H6Cl6 (Hexa Chloro Cyclo Hexane)
    When benzene is treated with Cl2, Br2 in dark or with aqueous KMnO4 or with dilute acids, no reaction     occurs.
CONCLUSION
    From the above arguments it is clear that benzene is not an open chain hydrocarbon.
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