3.3.10 Aromatic Chemistry

Question 1

what is the shape and angle of benzene?

Answer 1

planar, 120 degrees

Question 2

what mechanism(s) does benzene undergo?

Answer 2

electrophilic substitution

Question 3

why are arenes very stable?

Answer 3

due to the delocalisation of π electrons in the ring

Question 4

what reagents are used during the nitration of benzene?

Answer 4

concentrated nitric acid and concentrated sulfuric acid

Question 5

is benzene more or less stable than cyclohexa-1,3,5-triene? why?

Answer 5

• benzene is more stable due to the delocalised electrons in the ring
• ΔHydrogenation of cyclo = -120 (1 double bond); for benzene it should be -360 (supposedly 3 double bonds), but it’s actual value is -208
• therefore more energy is needed to break the bonds in benzene than cyclohexa-1,3,5-triene

Question 6

what is benzene typically used for?

Answer 6

pharmaceuticals + dyes

Question 7

how to form the electrophile in Friedel-Crafts acylation?

Answer 7

R-COCl + AlCl3 -> R-CO+ + AlCl4+

Question 8

how do you form the electrophile in the nitration of benzene?

Answer 8

• H2SO4 + HNO3 -> H2NO3(+) + HSO4(-)
• H2NO3(+) -> NO2+ + H2O

Question 9

what temperature do you use when undergoing the nitration of benzene and what happens above or below this temperature?

Answer 9

• 55 degrees Celsius; above this temperature = multiple substitutions
• below this temperature = ensures only one substitution

Question 10

what are nitrobenzene compounds used in?

Answer 10

explosives (TNT = trinitrotoluene)