benzene

Question 1

who created the first model of benzene

Answer 1

August Kekule

Question 2

describe benzenes reactivity

Answer 2

Benzene has a low reactivity as it does not take part in electrophilic addition reactions since:
the 2 forms were in a rapid equilibrium so an approaching Br2 molecule could not get attracted to a π bond before the structure changed

Question 3

how did kekule solve the bond length discrepancy for benzene

Answer 3

he discovered that all carbon - carbon bonds in benzene are the same length
so a C=C bond length was the same as a C-C bond length

Question 4

what does the circle represent in the second model of benzene

Answer 4

it represents the multiple π bonds in benzene which are alternating rapidly and in a rapid equilibrium so cannot be in a fixed position is represented simply as a circle

Question 5

what is the EXPECTED enthalpy change of hydrogenation of benzene, explain

Answer 5

expected to be -357 kJ mol^-1 since the enthalpy change of cyclohexene is -119 so it WAS safe to assume that it should be -119 x 3 since benzene has three more π bonds than cyclohexene

Question 6

what is the ACTUAL enthalpy change of hydrogenation of benzene

Answer 6

the actual enthalpy change of hydrogenation of benzene is -208 kJ mol^-1

Question 7

what does the enthalpy change of hydrogenation of benzene prove

Answer 7

the enthalpy change of hydrogenation proves that benzene is more stable than expected since -208 < -357. Also this shows that the enthalpy change is less exothermic than expected

Question 8

what are the reagents and conditions for the alkylation of benzene

Answer 8

reagents: halogenalkane & ANHYDROUS AlCl3
conditions: room temp

Question 9

complete the equation _ _ _ _ + C2H5Cl -> _ _ _ _ _ _ _ _ + HCl
and name the electrophile

Answer 9

C6H6 & C6H5C2H5
electrophile is C2H5

Question 10

how does one determine the electrophile when a molecule is bonded to benzene

Answer 10

whatever is on the end of the equation

Question 11

what are the reagents and conditions for the nitration of benzene

Answer 11

reagents: conc. nitric acid & conc sulphuric acid
conditions: refluc at 55°C

Question 12

what are the reagents and conditions for the halogenation of benzene

Answer 12

reagents: Cl & a halogen carrier (catalyst)
conditions: reflux with a halogen carrier (feCl3, AlCl3)