aromatic chemistry Flashcards
describe the bonding in the kekule structure of benzene
localised, alternating pi bonds formed from the sideways overlap of p orbitals forming 3 pi bonds
describe the bonding in the delocalised model of benzene
all six pairs of p orbitals overlap to form a delocalised ring structure
how would you expect benzene to react based on the kekule model
reactive and decolourise bromine
what was actually found about the reactivity of benzene
unreactive and requires a halogen carrier catalyst
what would you expect the bond lengths to be in benzene based on the kekule structure
alternating forming an irregular hexagon based on that C- C bond lengths are greater than C=C
what was actually found in terms of bond lengths in benzene
all the same length forming a regular hexagon intermediate of that of C-C and C=C
what would you expect the enthalpy of hydrogenation of benzene to be based on the kekule structure
3x that of cyclohexene due to having 3 C=C bonds
what was actually found regarding the enthalpy of hydrogenation of benzene
less exothermic than expected as it is more stable
what type of reaction is the nitration of benzene
electrophilic substitution
what is the functional group change in the nitration of benzene
benzene - nitrobenzene
what are the conditions and reagents for the nitration of benzene
conc HNO3 and conc H2SO4 catalyst
write the equation for the formation of nitrobenzene from benzene
benzene + HNO3 -> nitrobenzene + H2O
what is the electrophile in the nitration of benzene
NO2+
what type of reaction is the halogenation of benzene
electrophilic substitution
what are the conditions and reagents for the bromination of benzene
AlBr3 + Br2
what is the electrophile in the bromination of benzene
Br+
what type of reactions are alkylation and acylation of benzene
friedel crafts electrophilic substitution
why are friedel crafts reactions important in organic synthesis
formation of C-C bond by extending the carbon chain
what are the conditions and reagents for alkylation of benzene
AlCl3 and a chloroalkane
what is the electrophile in the alkylation of benzene forming ethylbenzene
CH3CH2+
what are the conditions and reagents for acylation of benzene
AlCl3 and an acyl chloride
what does acylation of benzene form
phenyl ketone
why are alkenes more reactive than benzene
benzene has a delocalised pi ring whereas alkenes have localised electrons, this gives them more electron density making them more susceptible to electrophilic attack
what is a phenol
a weak acid where a hydroxyl group is directly bonded to a benzene ring
as phenol is a weak acid, what does it react with
metals and metal hydroxides but NOT carbonates
what is the name of the salt formed when phenol reacts with sodium hydroxide
sodium phenoxide
why is phenol more reactive than benzene
the oxygen lone pair from the hydroxyl group partially delocalises into the pi ring which increases electron density making it more susceptible to electrophilic attack
how can you see phenol is more reactive than benzene through its halogenation reactions
no halogen carrier catalyst required
how can you tell phenol is more reactive than benzene through its nitration reactions
reacts with dilute HNO3 and no H2SO4 catalyst needed
what is the product formed from the bromination of phenol
2,4,6-tribromophenol
write the overall equation for the bromination of phenol
phenol + 3Br2 -> 2,4,6-tribromophenol + 3HBr
what are the products for the nitration of phenol
2-nitrophenol and 4-nitrophenol
why does the nitration of phenol produce a mixture of products
due to the directing effect
what are electron donating groups
-OH and -NH2
what are electron withdrawing groups
-NO2
