Aromatic chemistry

Question 1

what is nitration an important step in?

Answer 1

synthesis - the manufacture of explosives (TNT) and amines

Question 2

what is the structure of benzene?

Answer 2

a ring of 6 carbon atoms and a ring of delocalised electrons (C6H6)

Question 3

what is the bond length of the bonds in the benzene ring?

Answer 3

between single bonds and double bonds (an intermediate length)

Question 4

why is benzene so stable?

Answer 4

due to the delocalised electron ring

Question 5

why do substitution reactions occur in preference to addition reactions with benzene?

Answer 5

because addition reactions would involve breaking the ring of delocalised electrons

Question 6

why is benzene susceptible to attacks from electrophiles?

Answer 6

because the ring of delocalised electrons is an area of high electron density

Question 7

generation of the NO2+ electrophile (nitration)

Answer 7

H2SO4 + HNO3 –> NO2+ + HSO4- + H2O

Question 8

generation of the RCO+ electrophile (Friedel-crafts acylation)

Answer 8

RCOCl + AlCl3 –> RCO+ + AlCl4-

Question 9

what is the role of AlCl3 in Friedel-Crafts acylation?

Answer 9

a catalyst
it is regenerated: AlCl4- + H+ –> AlCL3 + HCl

Question 10

what is the thermochemical evidence for the stability of benzene?

Answer 10

the enthalpy change for the hydrogenation of cyclohexene is -120kjmol-1

so in theory the enthalpy of hydrogenation of benzene would be 3 x -120 = -360kjmol-1

but in reality it is -208kjmol-1