aromatic chemistry

Question 1

nature of bonding, shape and stability in a benzene ring

Answer 1

bonding:
each C has 3 covalent bonds
spare electrons in a p orbital overlap to form pi cloud
delocisation of electrons
shape:
hexagon
planar structure
C-C bonds between single and double bond length
stability:
expected ¬H hydrogenation of cyclohexatriene = -360 kJ mol-1
¬H hydrogenation benzene is less exothermic by 152kJ mol-1
benzene in more stable

Question 2

explain why substitution reactions occur in preference to addition reactions for aromatic compounds

Answer 2

the aromatic ring is very stable so energy has to be put in to break the ring this means in almost all reactions the ring remains intact

Question 3

electrophyllic attack on benzene ring results in

Answer 3

subsistution

Question 4

nitration is an important step in

Answer 4

synthesis including the explosives and formation of amines

Question 5

Friedel-crafts acylation reactions are

Answer 5

important steps in synthesis

Question 6

nitration mechanism, reagent and formation of nitronium ion

Answer 6

electrophilic subsistion
reagent: conc H2SO4 (catalyst) and conc HNO3
forming of +NO2 is
H2SO4 +HNO3 –> HSO4- + H2O + NO2+
benzene ring highly electron dense so electrons move to +NO2 this opens the ring causing it to have a + charge and NO2 bonded, electrons from H bond with ring moves into ring reforming the ring

Question 7

nitration overall equation

Answer 7

C6H6 + HNO3 –> nitrobenzene + H2O

Question 8

acyaltion mechanism, reagent and forming of electrophile

Answer 8

electrophyllic subsitution
reagent: acyl chloride and catalyst AlCl3
forming electrophile: ROCl + AlCl3 –> RCO+ +AlCl4-
benzene ring highly electron dense so electrons move to RCO+ this opens the ring causing it to have a + charge and RCO bonded, electrons from H bond with ring moves into ring reforming the ring

Question 9

acylation overall eqaution

Answer 9

acylation overall equation
benzene + CH3COCl –> phenyl(..)anone +HCl