Benzene Flashcards
(20 cards)
Evidence to disprove kekules structure
Lack of reactivity (doesn’t undergo electrophilic addition)- no reaction with bromine water
Benzene bond lengths all same
Hydrogenation 3x cyclohexene only -208kjmol-1
Delocalised model of benzene
adjacent p orbitals overlap sideways below and above the plane creates pi bonds forming ring of electron density
Delocalised ring
Phenol as an acid
Less soluble in water due to presence of non polar benzene ring
Ability to partially dissociate to produce h+ ions and Phenoxide ion
Why are phenols more reactive than benzene
Increased reactivity caused by lone pair of e- in oxygen p orbital donated into the pi system - electron density increases and attracts electrophiles more strongly
- nh2 directing
2,4,6
-no2 directing
3
-OH directing
2,4,6
Halogen directing
2,4,6
-cooh directing
3
CN directing
3
Benzene ring attached to 7 or more carbon chain or alkyl chain w func group
A substitutent
Prefix is phenyl
Reactions of benzene
Substitution reactions
Benzene reacts w electrophiles
Electrophilic substitution
Nitration of benzene
Reacts w nitric acid conc
H2SO4 and 50 degrees
Forms nitrobenzene and water
HNO3 + H2SO4=>NO2+ + HSO4- + H2O
Halogenating of benzene
Halogen carrier required to react
Electrophilic substitution
Benzene too stable to react w Br2
Br2 + FeBr3 => FeBr4- + Br+
Bromobenzene and H+ form
FeBr4- + H+ => FeBr3 + HBr
Alkylating of benzene
AlCl3 acts as catalyst
Haloalkane with AlCl3 forms electrophile
Forms HCl and xxthylbenzene
Acylation of benzene
Electrophilic sub of acyl chloride
Requires halogen carrier to form an electrophile
Forms phenylxxanone and HCl
Phenols
OH group attached to benzene ring
Phenol weak acid reactions
+NaOH
Forms Sodium phenoxide salt and H2O
Bromination of phenol
Br2 (aq)
Forms white pp = 2,4,6- tribromophenol and 3HBr
Orange to colourless
Nitration of phenol
With HNO3 dilute
Forms 2/4-nitrophenol and water
