Organic Chemistry: Arenes Flashcards
What is the formula of benzene?
C6H6
What were the problems with the aliphatic compounds proposed for benzene?
Failed to react with bromine even when heated
Would produce many monosubstituted compounds due to lack of rotation around bonds yet only one form of chlorobenzene and bromobenzene have been isolated
What was the Kekule model?
A ring with alternate double and single bonds
What were the problems with the Kekule model?
Double bonds means that it would readily undergo addition reactions yet it generally undergoes substitutions
Theoretical value much higher than actual enthalpy which shows that structure is actually more stable
What is the arrangement of electrons in benzene?
Each C forms single sigma bond with 2 others
Each C has one p orbital containing single electron which forms two single rings, one above and one below the sigma framework
How is an aromatic compound named when benzene is regarded as a side chain?
In the same way as alkyl groups, it is known as the phenyl group C6H5-
How are molecules of benzene with 1 substitution named?
Phenol, chlorobenzene, methylbenzene
Molecule is symmetrical so the location isn’t included in the name
How are molecules of benzene with 2 substitutions named?
One group is assumed to be attached to carbon atom 1 and the other to different carbon atoms to give the lowest number
1,3-dimethylbenzene
What are the observations for the combustion of benzene? Why?
A large amount of oxygen is required so it generally undergoes incomplete combustion
Orange, smokey flame is produced
Used as a test for unsaturated compounds
Reaction of benzene with hydrogen
Mixed with hydrogen in the presence of a Roney nickel catalyst at 150 degrees C
Produces cyclohexane
Addition reaction
Reaction of benzene with halogens
Addition reaction
Bromine in the presence of UV light
Forms 1,2,3,4,5,6-hexabromocyclohexane
Rapidity suggests its a free-radical reaction
How does a substitution reaction occur with benzene?
Attack on the ring by electrophiles
As it is very stable, a strong electrophile is required
What is the electrophile, the product and the mechanism of the reaction of benzene with fuming sulphuric acid?
Electrophile is SO3 Benzene sulphuric acid Pi electrons form bond with S and S breaks bond with O Forms Wayland intermediate H gives electrons to positive ring O and H form bond
What is the nitration mixture?
H2SO4 + HNO3 –> NO2+ +H2O + HSO4-
What is the electrophile, method and product of the nitration of benzene?
Electrohphile is NO2+
Round bottom flask held in beaker of cold water and benzene mixture is added slowly
Exothermic reaction and must be kept below 55 degrees to avoid multiple substitutions
H+ and benzene with NO2 attached and
