VJC 2025 Organic Compounds Tutorial

1 Victoria Junior College Organic Chemistry Tutorial: Nitrogen Compounds [H2 Only] SELF-CHECK EXERCISE a) Complete the following tables. Reactant Reaction Type, Reagents & Conditions Intermediate Reaction Type, Reagents & Conditions Products Nucleophilic substitution excess NH3, heat in a sealed tube CH3CH2NH2 ethylamine Nucleophilic substitution CH3CH2Cl, heat Condensation CH3COCl Reduction  LiA lH4 in dry ether Neutralisation HCl Neutralisation RCO2H Reduction  H 2, Ni catalyst, heat  H 2, Pt catalyst  LiA lH4 in dry ether Reactant Reaction Type, Reagents & Conditions Intermediate Reaction Type, Reagents & Conditions Products Reduction Sn and concentrated HCl, heat then add alkali such as NaOH(aq) phenylamine Nucleophilic substitution CH3CH2Cl, heat Condensation CH3COCl Neutralisation HCl Electrophilic substitution Br2(aq)

2 Reactant Reaction Type, Reagents & Conditions Intermediate Reaction Type, Reagents & Conditions Products Nucleophilic substitution Concentrated NH3 CH3CONH2 ethanamide Acid hydrolysis HCl(aq), heat Base hydrolysis NaOH(aq), heat Reduction LiAlH4 in dry ether b) Write down the organic compounds in the following mind map. OH―(aq) OH―(aq) heat NH3 Concentrated NH3 CH3CONH2 H+(aq), heat LiAlH4 in dy ether NH3(alc), heat H+(aq) NH3(alc) heat, excess CH 3CH2Cl CH3COCl OH―(aq)

3 c) Tick the functional groups that would be reduced. Reducing agents Alkene RCHO RCOR RCO 2H RCONH 2 RCN Nitrobenzene LiAlH4 in dry ether H2, Pt NaBH4 in methanol Sn in concentrated HCl, heat, followed by NaOH d) State the type of reactions that would occur. Reagents & conditions Alkene RX 1o or 2o ROH RCHO RCOR RCO 2H RCONH2 RCN RCOCl KMnO4, H2SO4(aq), heat K2Cr2O7, H2SO4(aq), heat OH▬(aq), heat H2O Relative basicities of amines Recall: Based on availability of lone pair of electrons on N (as Lewis base)  Basic strength increases when the lone pair of electrons on N is more available for donation to an acid.  Factors that affect availability of lone electron pair on N: - Inductive effect - Delocalisation (resonance effect) - Steric hindrance – block acid from approaching the N atom

4 1 (a) Suggest and explain the relative basicities of methylamine and ethylamine in gaseous state in terms of Lewis bases. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………[3] (b) Explain in terms of structures why ammonia is a stronger base than phenylamine but a weaker base than methylamine in aqueous state. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………[2] (c) 4–methylphenylamine and benzylamine are isomers. (i) Suggest how the basicity of 4–methylphenylamine might compare to that of phenylamine, and how the basicity of benzylamine might compare to that of ethylamine. Give reasons for your answers. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………[4] (ii) Suggest how bromine water could be used to distinguish between 4–methylphenylamine and benzylamine. State any observations you would make with each compound, and write balanced equations for any reactions that might occur. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………[2]

5 Each of these compounds can be made from methylbenzene in two steps. (iii) State reagents and conditions for each of the two steps in these two routes, and give the structures of the intermediate compounds. [6] (d) pK b values of three amines in aqueous solution are shown below. Suggest and explain the relative basicity of these amines in aqueous solution. Amines pKb CH3NH2 3.34 (CH3)2NH 3.27 (CH3)3N 4.20 ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………[3]

6 2 Why are amides, RCONH 2, less basic than amines, RNH2? A Amides form a zwitterion in which the nitrogen atom carries a positive charge. B Amides have a resonance structure involving the movement of a pair of electrons from the nitrogen atom to the oxygen atom. C Electrons on the nitrogen atom move on to the C–N bond giving it some double bond character so that it is more difficult to break. D The amide carbonyl group withdraws electrons from the NH 2 group to make the hydrogen atoms acidic. 3 Which compounds liberate ammonia when boiled with aqueous sodium hydroxide? 1 CH 3CH2NH2 2 CH 3CH2CONH2 3 CH 3CH2CO2NH4 4 Aspartame is widely used as a sweetener in canned drinks. Which compound would be a product of its hydrolysis? A CH 3CO2H B HO 2CCH2CO2H C D 5(a) Describe the conditions needed to hydrolyse amides in the laboratory. ……………………………………………………………………………………………………[1] (b) Predict the products of the hydrolysis of the amide groups in the following two drugs.

7 [4] 6(a) (i) Histamine is structurally similar to histidine in that it also contains the planar imidazole ring. Suggest the type of hybrid orbitals the lone pair of electrons occupy on N labelled (a) and (b). Hence, account for their relative basicity. You may assume that the NH in the imidazole ring is inert. ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… ……………………………………………………………………………………………………… …………………………………………………… ……………………………………………...[2] (ii) Hence, predict the structural formula of the organic product formed when 1 mol of histamine reacts with (I) 1 mol of HC l(aq) (II) 2 mol of HBr(aq) [2] (b) Like histidine, compound A contains a 5–membered ring with more than one kind of atom. Draw the structural formula of the organic products formed when compound A is treated with the following reagents and state clearly the type of reaction that has taken place.

8 (i) hot NaMnO4 / NaOH(aq) (ii) ethanoyl chloride 7 The R group of aspartic acid is –CH 2CO2H. The three pKa values associated with aspartic acid are 1.88, 3.65 and 9.60. Which form would be predominant at pH 2.7? A H 2NCH(CH2CO2-)CO2- B H 3N+CH(CH2CO2-)CO2- C H 3N+CH(CH2CO2H)CO2- D H 3N+CH(CH2CO2H)CO2H 8 An amino acid residue of structure H 2NCH(CH2CO2H)CO2H was isolated after partial hydrolysis of an animal protein. Which form would be predominant at pH 12? A H 2NCH(CH2CO2-)CO2- B H 3N+CH(CH2CO2-)CO2- C H 3N+CH(CH2CO2H)CO2- D H 3N+CH(CH2CO2H)CO2H 9 The sequence of amino acids (primary structure) of a polypeptide A can be determined by analysing the fragments obtained from different enzymatic hydrolysis. The following fragments were obtained when A was hydrolysed using enzyme chymotrypsin which digests proteins at carboxylic acid end of phenylalanine, phe. gly – lys – phe val – lys – phe tyr