3.10 Aromatics Flashcards
b) outline a mechanism for the reaction of this electrophile with benzene to form p and name mechanism
Propanoyl chloride + AlCl3 -> AlCl4^- + CH3CH2CO^+
Name of mechanism : electrophilic substitution
Compound Q is an isomer of P that shows optical isomerism. Q forms a silver mirror when added to a suitable reagent. Identify this reagent and suggest a structure for Q
Tollens reagent
C6H6 + CH3CH2COCl -> C6H5 COCH2CH3 + HCl
Organic product = phenylpropanone
Catalyst = AlCl3
CH3CH2COCl + AlCl3 -> CH3CH2CO^+ + AlCl4^-
AlCl4^- + H^+ -> AlCl3 + HCl
Write an equation for the reaction of propanal with HCN and name the product.
CH3CH2CHO + HCN → CH3CH2CH(OH)CN
2-hydroxybutanenitrile
Name and outline a mechanism for this reaction of propanal with HCN
Suggest how the rate of reaction of propanone with HCN would compare with the rate of reaction of propanal with HCN Explain your answer
- propanal faster
- propanal has one alkyl (CH3) group donating electrons via the inductive effect, propanone has two
- this makes carbonly carbon in propanal more electrophilic and more susceptible to nucleophilic attack by CN^−
- propanal easier to attack at end of chain
Benzene is more stable than cyclohexatriene
Expected hydrogenation of C6H6 = 3(-120) =-360
Actually hydrogenation of benzene is 152 kJ mol^-1 less exothermic
Because of delocalisation
Reagent = Conc HNO3, Conc H2SO4
H2SO4 + HNO3 -> HSO4^- + NO2^+ + H2O
Give the reagents used to produce the electrophile in a benzene reaction. Write an equation or equations to show the formation of this electrophile.
Reagents :
Conc HNO3
Conc H2SO4
H2SO4 + HNO3 -> HSO4– + NO2+ + H2O
Only part ii)
Name the product, C6H5COCH3.
phenylethanone
Just the mechanism
b) When methylbenzene reacts with ethanoyl chloride and aluminium chloride, a similar substitution reaction occurs but the reaction is faster than the reaction of benzene. Suggest why the reaction of methylbenzene is faster.
-methyl group has (positive) inductive effect OR increases electron density on benzene ring OR pushes electrons OR is electron releasing
- electrophile attracted more
or benzene ring better nucleophile
The product of the substitution reaction (C6H5COCH3) was analysed by mass spectrometry. The most abundant fragment ion gave a peak in the mass spectrum with m/z = 105. Draw the structure of this fragment ion.
Reducing agent = H2
Empirical formula = CH2
Angle in benzene = 120 degrees
Angle in cyclohexane = 109.5 degrees
If ammonia is a nucleophile, why would a reaction between ammonia and benzene be unexpected
Benzene repels nucleophiles
Enthalpy of hydrogenation of cyclohexene is -120kJ mol^-1
x,y,w
I) -240
ii) anywhere between -121 & -239
iii) for 1,3 C=C, bonds are closer together as there are some overlap of electrons, Pi clouds or p orbitals / some delocalisation for 1,3 C=C
Enthalpy of hydrogenation of cyclohexene is -120kJ mol^-1
x,y,w
I) -240
ii) anywhere between -121 & -239
iii) for 1,3 C=C, bonds are closer together as there are some overlap of electrons, Pi clouds or p orbitals / some delocalisation for 1,3 C=C
- don’t do mechanism
Electrophile in picture
reagent : acidified silver nitrate
P : no reaction
Q : white precipitate
Mr product = 135
Expected mass = 5.05 x 135 / 98 = 7.33 g
Percentage yield = 4.82 / 7.33 = 65.8%
Skip part a
Name and outline a mechanism for the reaction when a specific specic reacts with nitrobenzene to form 1,3-dinitrobenzene.
