AC3: Aromatic Compoudns Flashcards
What is an aromatic compound/arene
a compound that contains at least one benzene ring
What is the molecular formula of benzene
C6H6
describe the properties of benzene
colourless, sweet-smelling, highly flammable, carcinogenic
What is benzene found in that makes it carcinogenic (2 things)
cigarette smoke and crude oil
Describe the Kekulé model for the structure of benzene
hexagonal ring with alternate alkene-like double bonds (3 double bonds in total)
Describe and explain the 3 pieces of evidence that suggest the Kekulé model for the structure benzene is incorrect
1 - Benzene does not react readily with halogens in the dark without a catalyst. Suggest that benzene does not have any alkene-like double bonds
2 - C-C bond lengths in benzene are all the same, and are between the lengths of a single C-C bond and double C=C bond
3 - Enthalpy of hydrogenation of benzene is less exothermic than enthalpy of hydrogenation of hypothetical cyclic triene (Kekulé) structure. Suggests that benzene is more stable than Kekulé structure
What is the modern accepted model for the structure of benzene
The delocalised π - electron system model
Describe the delocalised π - electron system
sideways overlap of p-orbitals above and below the plane of the carbon ring results in a delocalised π - electron system
If an alkyl group has ≥ 7 carbons, what would the name of the prefix be when naming the benzene part
phenyl
Why does Benzene undergo substitution rather than addition?
Undergoing an addition reaction will destroy the sideways overlap of the p-orbitals in the delocalised π - electron system, which is stable ∴ is not a favourable process. Whereas the delocalised π - electron system is retained via a substitution reaction
Why is benzene less reactive than alkenes?
The electron density of the delocalised π - electron system is lower than that of a localised π - bond in an alkene. so the delocalised π - electron system is less attractive to electrophiles / less able to induce a large dipole in Br2
Compare the reactivity between benzene and alkenes
benzene is less reactive than alkenes
Can benzene undergo addition reactions? if not, what can it undergo
no, undergoes substitution
What is the mechanism for benzene undergoing a substitution reaction
Electrophilic substitution
What is the catalyst used for a benzene halogenation reaction and what do you call this type of catalyst
AlBr3 or FeBr3
halogen carriers
