Ch.25 Aromatic Compounds
No description yet. This curated deck is ready for daily study.
Card preview (24)
What evidence disproves kekules benzene model
. Does not decolourise bromine in an electrophilic addition reaction . Each bond was the same length, between a single and double . Enthalpy change of hydrogenation is too low
What is the formula of a nitro group
-NO2
When does benzene become a substituent
When attached to an alkyl group with a functional group or more than 7 carbons
What is the prefix used for a benzene ring
Phenyl
Benzene with a carboxyl
Benzoic acid
Benzene with an amine (NH2) group
Phenylamine
Benzene and an aldehyde (CHO) group
Benzaldehyde
Nitration of benzene
with nitric acid Forms nitrobenzene Catalysed by sulphuric acid and heated to 50 degree C
Halogenation of benzene
Benzene does not react with halogens unless a halogen carrier catalyst is present (AlCl3)
freidel-crafts Alkylation reactions
Reacting benzene with a haloalkane in the presence of AlCl3 which acts as a halogen carrier catalyst generating the electrophile
Phenol
Benzene with an -OH group
Is phenol or alcohol less soluble
Phenol due to the presence of the non polar benzene ring
When dissolved in water phenol partially dissociates in water to form what
Phenoxide ion and a proton therefor phenol is a weak acid
Phenol and bromine water
Forms white precipitate and decolourises
Compare the reactivity of phenol and benzene
Increased reactivity of phenol is due to an oxygen lone pair being donated into the pi system increasing the electron density attracting electrophiles more than benzene. Therefore the aromatic ring in phenol is more susceptible to attack from electrophiles than in benzene
Compare acidity of alcohols phenols and carboxylic acids
Alcohols don’t react with NaOH or Na2CO3 least acidic Phenols only react with NaOH middle Carboxylic acids react with both most acidic
the kekule model
six c ring with alternating single and double bonds
delocalised benzene model
planar, cyclic, hexagonal hydrocarbon 3 of 4 e- bond to 2 c and 1 h remaining 1 is in a p orbital in a right angle to the plane adjacent p orbitals overlap sideways in both directions above and bellow the plane of the ring to form a ring of electron density this creates a pi bond system made up of 6 delocalised electrons spread over the 6 carbons
use and reformation of the catalyst in the nitration of benzene
HNO3 + H2SO4 —> NO2+ + HSO4- + H2O H+ + HSO4- —> H2SO4
use and reformation of catalyst in bromination of bezene
Br2 + FeBr3 —> FeBr4- + Br+ H+ + FeBr4- —> FeBr3 + HBr
benzene undergoes what type of reaction
electrophilic substitution
freidel-crafts acylation reactions
when benzene reacts with an acyl chloride in the presence of an AlCl3 an aromatic ketone is formed
bromine and cyclohexene
pi bond in alken has localised e-‘s above and bellow plane in area of high electron density this induces a dipole in the non-polar bromine the slight + bromine enables the bromine molecule to act as an electrophile
why doesn’t benzene react with bromine alone
delocalised pi e-‘s are spread so not as e- dense and a C=C bond in a alkene insufficient pi e- density around any 2 C’s to polarise the non-polar bromine