Why straight chain structure of benzene is not possible?What is the evidence of cyclic structure of benzene?

Question

Why benzene show peculiar behaviour?
Why it do addition reactions like alkenes?
Why it undergoes electrophilic substitution reaction?

Answer 1

1. The molecular formula of benzene is C6H6. This is a formula of the type CnH2n-6. If there were no rings or double or triple bonds, the formula type would be CnH2n+2. Each difference of 2 in the H's is called a point of unsaturation. Thus benzene has four points of unsaturation. It is not possible to write a structure of benzene without at least one ring.

2. Benzene behaves as it does because it has a full molecular shell of electrons, just as rare gases atoms have complete atomic shells. Thus benzene acts in a way that restores the completed shell.

3. Benzene does not undergo addition reactions like alkenes. One exception is complete reaction with chlorine to form C6H12, dodecachlorocyclohexane.

4. Electrophilic substitution begins with an addition, then restores the complete electronic shell:

C6H6 + Br2 ===> C6H6Br+ + Br-
C6H6Br+ ===> C6H5Br + HBr

(That first step needs Fe or FeBr2 catalyst to go.)

Answer 2

Consider a straight chain structure for benzene and further assuming that each cabon carries one H-atom it should be capable of forming three mono substitution products .Benzene yields only one mono substituent product.

Answer 3

i have drawn the straight chain structure of benzene
can anyone plzz help me out why this structure is not possible?? :P

CH3-C---C-C---C-CH3

(- represting bonds --- means triple bonds)