3.3.10 aromatic chemistry Flashcards
the reaction between propanoyl chloride and benzene is an example of acylation
Which is correct representation of part of the mechanism for this reaction?
C
The nitration of benzene uses a nitrating mixture of concentrated nitric acid and concentrated sulfuric acid
Which statement is correct
a) HNO3 acts as a base
b) HNO3 acts as a catalyst
c) HNO3 acts as an electrophile
d) HNO3 acts as a reducing agent
A
Use your understanding of the bonding in benzene to identify the compound that has the most exothermic enthalpy of hydrogenation
A
Paracetamol is a medicine commonly used to relieve mild pain
Traditionally, paracetamol has been made industrially in a three step synthesis from phenol
Name the mechanism in step 1
electrophilic substitution
In practice, ethanoic anhydride is used in the industrial synthesis rather than ethanoyl chloride
Give one reason why ethanoyl chloride is not used in the industrial synthesis
corrosive
Explain the bonding in and the shape of a benzene molecule. Compare the stability in benzene with that of the hypothetical cyclohexa-1,3,5-triene molecule
Use the data in your answer
(6 marks)
Stage 1:
1a) each C has three covalent bonds
1b) spare electrons in a p orbital overlap to form a pi bond
1c) delocalisation
Stage 2:
2a) planar
2b) hexagon
2c) C-C bonds equal in length
Stage 3:
3a) expected hydrogenation of cyclohexatriene =-360kJ mol
3b) hydrogenation benzene is less exothermic
3c) benzene lower in energy than cyclohexatriene
The enthalpy of hydrogenation of cyclohexa-1,3-diene is not exactly double that of cyclohexene
Suggest a flue for the enthalpy of hydrogenation of cyclohexa-1,3-diene and justify your value (3 marks)
M1: value within range -239 to -121
M2: double bonds separated by one single bond
M3: allows some delocalisation of p orbitals
Write an equation for the reaction of concentrated nitric acid with concentrated sulfuric acid to form the species that reacts with nitrobenzene
HNO3 + 2H2SO4 — NO2+ + H3O+ + 2HSO4-
Use the chromatogram in the diagram above to deduce the Rf value of 1,4-dinitrobenzene in this experiment
a) 0.41
b) 0.46
c) 0.52
d) 0.62
D
State in general terms what determines the distance travelled by a spot in TLC
Balance between solubility in moving phrase and retention by stationary phase
To obtain the chromatogram, the TLC plate was held by the edges and placed in the solvent in the beaker in the fume cupboard. The lid was then replaced on the beaker.
Give one other practical requirement when placing the plate in the beaker
solvent depth must be below start line
State in terms of its bonding why benzene is more stable than cyclohexa-1,3,5-triene
electrons delocalised
Write the letters w x and y in order of increasing bond length
x y w
