AS & A Level Chemistry 34.3 Amides: Exam Style Questions Paper 4

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Question

(a) Compare and explain the relative acidities of butanoic acid, ethanol, ethanoic acid and water.

(b) Three carboxylic acids, methanoic acid, HCO2H, ethanedioic acid, HO2CCO2H, and butanedioic acid, HO2CCH2CH2CO2H, are compared. Two tests were carried out on separate samples of each organic acid, as shown.

        The following results were obtained. ✔= observed change 🗙 = no observed reaction

(i) Complete the table with the reagents and conditions and the observed change for a      positive test.       Assume these organic acids all have a similar acid strength.                                                                                                                                                                                                                                                                                                         

  (ii)  Each compound, HCO2H, HO2CCO2H and HO2CCH2CH2CO2H, is dissolved seperately in CDCl3. Proton (¹H) NMR and carbon-13 (¹³C) NMR                        spectra are then obtained.Complete the table.

(iii) The proton NMR spectrum of HCO2H in D2O is obtained.

         Describe and explain the difference observed between this spectrum and the proton NMR spectrum of HCO2H in (b)(ii).

(c) 1,4-dibromobutane, Br(CH2)4Br, is used in the synthesis of the dicarboxylic acid J and diamine K  as shown.

(i) Draw the structures of G and H in the boxes.

(ii) Suggest reagents and conditions for each of steps 1 to 4.

(d) Polyamide L can be synthesised from dicarboxylic acid J, HO2C(CH2)2CO2H, and diamine K,  H2N(CH2)6NH2.

      Draw the repeat unit of the polymer formed in the box. Any functional groups should be shown displayed.

Answer/Explanation

Answer:     (a) M1: ethanoic acid > butanoic acid > water > ethanol
                                  M2: a reason given in terms of an electron donating or an electron withdrawing group for one of:
                                  strengthening of O–H bond OR weakening of O–H bond OR stability of anion
                                 Two out of the three alternatives M3, M4 and M5:
                                  M3: ethanol: positive inductive effect / electron donating effect of ethyl / alkyl / R group
                                  M4: butanoic acid: positive inductive effect / electron donating effect of propyl / alkyl / R group
                                  M5: (either ethanoic or butanoic) acid: negative inductive effect of either C=O or carbonyl OR negative charge delocalised
                                 over COO–

(b)(i)

 

M1 / M2: reagents and conditions × 2
M3: observations both correct

(b)(ii)

one mark for three, four or five correct
two marks for six correct

(b)(iii) OH peak disappears AND proton / H exchanges with deuterium 1

(c)(i) G = HOCH2CH2CH2CH2OH
              H = NCCH2CH2CH2CH2CN

(c)(ii) M1: step 1 NaOH(aq) + heat

      M2: step 2 acidified KMnO4 + heat / acidified K2Cr2O7 + heat

      M3: step 3 CN– / KCN / NaCN + heat

      M4: step 4 LiAlH4 ALLOW Na in ethanol or H2 + Ni / Pd / Pt

(d) 

M1: correct displayed amide linkage

M2: the rest of the repeat unit correct including trailing bonds

Question

(a) Organochlorine compounds can undergo hydrolysis.
 
\(R-Cl + H_{2}O\rightarrow R-OH + HCl\)
 
       State and explain the relative rates of hydrolysis of the following compounds.
 

CH3CH2Cl           CH3COCl              C6H5Cl

(b) Epibatidine is a naturally occurring organochlorine compound.

(i) Epibatidine is a weak base.
 
     State what is meant by the term weak base.
 
      A molecule of epibatidine contains two nitrogen atoms, both of which can act as a base.
 
(ii) Epibatidine reacts with HCl(aq).
 
      Complete the structure to suggest the product formed in this reaction.

(c) Polyamides, such as nylon-6, can be prepared from a monomer that contains both an amine and an acyl chloride functional group.

(i) When the nylon-6 monomer is hydrolysed, bonds are broken and formed.

      By considering the two steps in the mechanism of the reaction, complete the table by  placing one tick (✔) in each row to indicate the types of bonds broken and formed during the mechanism.

(ii) Draw two repeat units of nylon-6. The amide bond should be shown fully displayed.

(d) An addition polymer made from two different alkene monomers is called a co-polymer. A section  of a polyalkene co-polymer is shown.

       Draw the structure of the two alkene monomers which produce this co-polymer.

(e) Explain why polyamides normally biodegrade more readily than polyalkenes.

(f) The alkene phenylethene can be prepared from benzene in three steps.

(i) Deduce the identity of compound H and draw its structure in the box.

(ii) Suggest reagents and conditions for each of the steps 1–3.

Answer/Explanation

Answer:     (a) M1: CH3COCl > CH3CH2Cl > C6H5Cl

        M2 & M3 any two from:
                                  • in C6H5Cl (no hydrolysis) C-Cl bond is part of delocalised system
                                      OR p-orbital on Cl overlaps with π system OR electrons from Cl overlap with π system
                                  • CH3COCl carbon in C-Cl bond is more electron deficient since it is also attached to an oxygen atom (ora)
                                      or C-Cl bond strength is weakest in CH3COCl (ora)
                                  • CH3CH2Cl carbon in C-Cl bond strengthened by positive inductive effect of alkyl group
 
(b)(i) partially ionised and proton acceptor
 
(b)(ii) 
 
(c)(i) 

(c)(ii) 

d) 

(e) C-C bonds are non-polar / polyalkenes cannot be hydrolysed and polyamides can be broken down by hydrolysis

(f)(i) 

(f)(ii) M1:              step 1:              CH3COCl + AlCl3

               M2:              step 2:               NaBH4 / LiAlH4

               M3:              step 3:               conc. H2SO4, heat 

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