Unit 4 Mechanisms

Question 1

Draw the mechanism for the acylation of benzene.

Answer 1

Arrow from benzene delocalised electron ring to carbocation.
Draw intermediate - must show horseshoe shape of delocalised ring (with + at centre) and the acyl group and H attached to benzene carbon at the open part of the horseshoe.
Arrow from C-H bond to horseshoe

Question 2

What catalyst is used for the acylation of benzene? Write all the equations that involve the catalyst.

Answer 2

AlCl3

AlCl3 + CH3CClO==> AlCl4- + CH3C=O+
AlCl4- + H+ ==> AlCl3 + HCl

Question 3

Draw the mechanism for the reaction between HCN and CH3CH2CHO. What type of mechanism is this?

Answer 3

Nucleophilic Addition

Arrow from lone pair on C of CN- to C with the C=O on the CH3CH2CHO molecule.
Arrow from C=O bond to O
Formation of intermediate with C-O-
Arrow from lone pair on O to H+ ion

Question 4

Draw and name a mechanism for the nitration of benzene.

Answer 4

Electrophilic Substitution

Arrow from benzene delocalised electron ring to N of NO2+
Draw intermediate - must show horseshoe shape of delocalised ring (with + at centre) and the NO2 group and H attached to benzene carbon at the open part of the horseshoe.
Arrow from C-H bond to horseshoe

Question 5

What are the reagents and what is the equation for the formation of the electrophile in the nitration of benzene?

Answer 5

Conc. H2SO4 and conc. HNO3

H2SO4 + HNO3 ==> HSO4- + H2O + NO2+

Question 6

Draw and name the mechanism for the reaction between ethanoyl chloride and NH3. What is the name of the organic product?

Answer 6

Nucleophilic addition/elimination

Arrow from lone pair on N of NH3 to C that has C=O on ethanoyl chloride
Arrow from C=O bond to O
Formation of intermediate with N+ and O-
Arrow from lone pair on O to C-O bond
Arrow from C-Cl bind to Cl
Arrow from N-H bond to N

Ethanamide

Question 7

Other that NH3, what reagents react with ethanoyl chloride and what products are formed?

Answer 7

H2O ==> carboxylic acid + HCl
Alcohol ==> ester + HCl
Primary amine ==> substituted amide + NH4Cl

Question 8

Draw and name the mechanism for the reduction of CH3COH with NaBH4 in acidic conditions. State what type of alcohol the product is.

Answer 8

Nucleophilic addition

Arrow from lone pair of H- (simification of NaBH4) to C with C=O
Arrow from C=O bond to O
Arrow from lone pair on O to H+(aq)

Primary alcohol

Question 9

Why do aldehydes and asymetrical ketones produce race ages in nucleophilic addition reactions?

Answer 9

They have chiral carbon centres but are planar molecules, so the nucleophilic can attack from two different directions, decided by chance.

Question 10

Does the product of a nucleophilic addition reaction with a symmetrical ketone rotate plane polarised light?

Answer 10

No. It has no chiral carbon centre as the alkyl groups on either side are the same.

Question 11

Draw and name the mechanism for the reaction between NaOH and CH3CH2Br when conditions are aqueous and warm

Answer 11

Nucleophilic Substitution

Arrow from lone pair on OH- formed from NaOH
Arrow from C-Br bond to Br

Question 12

Draw and name the mechanism for the reaction between NaOH and CH3CH2Br when in an ethanolic solution

Answer 12

Arrow from lone pair on OH- to H on C next to C with Br
Arrow from C-Br to neighbouring C-C bond.
Arrow from C-Br bond to Br