Flashcards in 25 Deck (13):
Why was Kekule's model disproved?
Hydrogenation energy is less exothermic than expected - benzene is more stable than Kekule's model
All bond lengths are equal
Lack of reactivity - bromine does not decolourise bromine water or undergo electrophilic addition
What type of reaction does benzene undergo?
Nitration of benzene
Conc HNO3 and conc H2SO4 (catalyst)
Halogenation of benzene
Halogen (Cl/Br) and halogen carrier (AlCl3, AlBr3, FeCl3, FeBr3, catalyst)
Friedel-crafts alkylation of benzene
Chloroalkane + AlCl3 (catalyst, anhydrous)
Friedel-crafts acylation of benzene
Acyl chloride + AlCl3 (catalyst, anhydrous)
Comparing reactivity: alkenes vs arenes
Benzene does not react with bromine without a halogen carrier due to the delocalised pi electrons which have a lower electron density than C=C and therefore cannot polarise Br2
What is phenol?
OH directly attached to C6H6
Non polar benzene ring makes phenol less soluble and is classified as a weak acid
When OH is attached to a side chain (benzene) it is classified as an alcohol
Phenol + NaOH
Salt + H2O
Phenol + 3Br2
2,4,6-tribromophenol + 3H2
Phenol + HNO3 (dilute)
Why does phenol react more readily than benzene?
Lone pair of electrons from the oxygen p orbital (OH) is donated in the pi system of phenol - increased electron density attracts electrophiles therefore more susceptible to attack. The electron density is sufficient enough to polarise bromine molecules