Aromatic Chemistry Flashcards
What are cyclic compounds also called?
Alicyclic - similar to branched compounds (aliphatic)
Outline the structure of cyclohexene
Cyclohexane but with 1 C=C
Outline the structure of Cyclohex-1,3,5-triene
Cyclohexane with 3 C=C at 1st, 3rd, 5th Cs
Outline the structure of Benzene
C6H6 - resonates between 1,3,5 or 2,4,6 triene - makes ring of delocalised e-
What did scientist predict the structure of benzene was with X-ray crystallography?
Predicted it had Kekule structure:
6C-H
3C=C shorter
3C-C longer
What was the actual structure of benzene with x-ray crystallography?
6C-H
6C=C (intermediate)
What did scientists predict Benzene’s structure as with the enthalpy of hydrogenation?
Cyclohexene + H2 -(Ni)-> Cyclohexane E = -120kJmol-1
Cyclohex-1,3,5-triene +3H2 -(Ni)-> Cyclohexane E=-360kJmol-1
What did scientists predict would happen with Benzene with bromination?
Decolourise Br(aq) like:
Cyclohex-1,3,5-triene
What actually happened when C6H6 reacted with Br (aq)?
No reaction - stayed orange
What happened when C6H6 reacted with Br (aq) with a catalyst? Why?
Electrophilic substitution (a reaction) occurred - catalyst maintained ring stability
Why did C6H6 react with Br (aq) with a catalyst only?
Ring of delocalised e- not dense enough to polarise Br2 - needed catalyst
What was the actual structure of Benzene with enthalpy change of hydrogenation
Benzene + 3H2 -> Cyclohexane E=-208kJmol-1 (less exo)
What is the only mechanism benzene undergoes? Why?
Electrophilic substitution - delocalised e- ring attract electrophiles
Outline all the electrophilic substitutions benzene can undergo
- Nitrates (-NO2)
- Amides (-NH2)
- Halogens (-Br/Cl)
- Haloalkanes (-CH3)
- Acyl compounds (-COCH3)
Outline the creation of the halogen electrophiles
AlBr3 + Br2 -> AlBr4- + Br+ (e- pair acceptor)
Outline the mechanism of the Halogen + benzene electrophilic substitution
- Br+ attacked by 2e- from e- ring
- H atom gives 2e- to partial e- ring - forms H+ ion
Outline the reformation reaction of the catalyst in halogen + C6H6 electrophile substitution
AlBr4- + H+ -> AlBr3 + HBr
Outline the overall reaction of C6H6 + halogen (Br) electrophilic substitution
C6H6 + Br2 -> C6H5Br
Outline the formation of the electrophile for the electrophilic substitution of C6H6 + Haloalkanes (C2H5Cl)
C2H5 + AlCl3 -> +C2H5 + AlCl4-
Outline the mechanism steps of the electrophilic substitution of haloalkanes (+C2H5)
- C6H6 e- ring attacks +C2H5
- H atom gives 2e- to partial e- ring of C6H6 -> forms H+ ion
Outline the reformation reaction of the catalyst for the electrophilic addition of C6H6 + haloalkane
AlCl4- + H+ -> AlCl3 + HCl
Outline the overall reaction of the electrophilic substitution of C6H6 + Haloalkane (C2H5Cl)
C6H6 + C2H5Cl -> C6H5C2H5 + HCl
Outline the formation of the electrophile for the electrophilic substitution of C6H6 & Nitrates
HNO3 + H2SO4 -> HSO4- + H2NO3+
H2NO3+ -> NO2+ + H2O
Outline the mechanism steps for C6H6 + NO2 (electrophilic substitution)
- C6H6 e- ring attacks NO2+
- H atom on C6H6NO2 gives e- pair to partial e- ring forming H+ ion
