ASRJC 2025 H2 Chem Nitrogen Compounds Notes

2025 JC2 H2 Nitrogen Compounds ©2025/ASRJC/CHEM 1 ANDERSON SERANGOON JUNIOR COLLEGE JC 2 H2 CHEMISTRY NITROGEN COMPOUNDS Content Resources 1 Amines 1.1 Structure & Classification 1.2 Nomenclature 1.3 Physical Properties of amines 1.4 Basic Properties of amines 1.5 Preparation of amines 1.6 Reactions of amines Lecture 1 • Mode: F2F • Lecture note: Pg 2 to 11 • SLS quiz: Q1 – 2 2 Amides 2.1 General formula & Structure 2.2 Nomenclature 2.3 Physical Properties of amides 2.4 Preparation of amides 2.5 Reactions of amides Lecture 2 • Mode: F2F • Lecture note: Pg 12 to 18 • SLS quiz: Q3 – 6 3 Amino Acids (continued) 3.1 Introduction to amino acid 3.2 General Properties of amino acids 4 Polypeptides and Proteins 4.1 Polypeptides 4.2 Hydrolysis of polypeptides/proteins Lecture 3 • Mode: F2F • Lecture note: Pg 18 to 30 • SLS quiz: Q7 – 10 LEARNING OUTCOMES Candidates should be able to: (a) describe the formation of amines as exemplified by ethylamine (through amide and nitrile reduction; see also Section 11.4) and by phenylamine (through the reduction of nitrobenzene) (b) describe the reaction of amines in the formation of salts (c) describe and explain the basicity of primary, secondary and tertiary amines in the gaseous phase (interpret as Lewis bases) (d) explain the relative basicities of ammonia, ethylamine and phenylamine in aqueous medium, in terms of their structures (e) describe the reaction of phenylamine with aqueous bromine (f) describe the formation of amides from the condensation reaction between RNH2 and R'COCl (g) explain why an amide is neutral in terms of delocalisation of the lone pair of electrons on nitrogen (h) describe the chemistry of amides, exemplified by the following reactions: • hydrolysis on treatment with aqueous alkali or acid • reduction to amines with lithium aluminium hydride (i) describe the acid/base properties of amino acids and the formation of zwitterions (j) describe the formation of peptide (amide) bonds between α-amino acids, and hence explain protein formation (k) describe the hydrolysis of proteins REFERENCES 1. Organic Chemistry; K. Peter C. Vollhardt 2. Organic Chemistry; Francis A. Carey 3. Organic Chemistry; Morrison and Boyd 4. Organic Chemistry; John McMurry 5. Chemistry In Action; Michael Freemantle 6. Chemistry; J.G.R. Briggs 7. Biology for Advanced Level; Glenn and Susan Toole 8. Principles of Biochemistry; David L. Nelson 9. H2 Chemistry Teaching and Learning Guide

2025 JC2 H2 Nitrogen Compounds ©2025/ASRJC/CHEM 2 1 AMINES 1.1 STRUCTURE & CLASSIFICATION ◼ Amines are organic derivatives of ammonia where one or more hydrogen atoms is/are replaced by the corresponding number of alkyl or aryl group(s). ◼ Can be classified according to their degree of substitution on the nitrogen atom (i.e. the number of R group substituents on the nitrogen atom) i.e. primary (1) – one group substituted on N atom secondary (2) – two groups substituted on N atom tertiary (3) – three groups substituted on N atom E.g. Class Functional Group Aliphatic amine Aromatic amine (N atom is directly bonded to the benzene ring) 1 −NH2 NCH3 H H e.g. ArNH2 e.g N H H 2 NH R2NH or RR’NH e.g. NH CH3CH2 CH3 Ar2NH or ArRNH N CH3 H e.g 3 N R3N or RR’R’’N e.g. N CH3 CH2CH3 CHCH3 CH3 Ar3N or Ar2RN or ArR’R’’N N CH3 CH2CH3 e.g ◼ Quaternary (4) ammonium compounds - four groups substituted on N atom which is tetravalent - named as ammonium salts E.g. tetramethylammonium chloride (CH3)4N Cl N HR H

2025 JC2 H2 Nitrogen Compounds ©2025/ASRJC/CHEM 3 1.2 NOMENCLATURE ◼ For simple amines - suffix –amine is added to the name of the alkyl group that is bonded to the N atom E.g. Alkylamines Arylamines CH3CH2NH2 ethylamine CH3CHCH2CH2CH3 NH2 2-pentylamine NH2 phenylamine NH2 cyclohexylamine CH2NH2 (phenylmethyl)amine / benzylamine CH2CH3 NH2 Br 5-bromo-2-ethylphenylamine* HN CH3 CH3 dimethylamine N CH3 H3C H3C trimethylamine N H diphenylamine *Recall: Substituents on the benzene ring are listed in alphabetical order and direction of num bering is governed by the usual rule “smallest possible numbers to the substituents”. ▪ For polyfunctional amines with other functional groups of higher priority, - treat the amine group as a substituent and add the prefix –amino to the parent compound E.g. H2NCH2COOH 2-aminoethanoic acid H2N OH 4-aminophenol ◼ For 2 and 3 amines with alkyl substituents on the nitrogen atom: - named as N- substituted derivatives of primary amines - the parent amine is taken to be the one with the longest carbon chain - the prefix N- is added to identify substituents on the amino nitrogen. E.g. CH3NHCH2CH3 N-methylethylamine CH3NCH2CH2CH3 CH3 N,N-dimethylpropylamine N CH3 CH2CH3 N-ethyl-N-methylphenylamine

2025 JC2 H2 Nitrogen Compounds ©2025/ASRJC/CHEM 4 1.3 PHYSICAL PROPERTIES OF AMINES (a) Boiling / Melting Points (SDL) ◼ Lower alkylamines are gases (with odours similar to ammonia) or low boiling liquids (with characteristic fishy smell). Amines with high molecular mass are solids. E.g. CH3NH2 b.p. = -7C (gas) CH3CH2NH2 b.p. = 17C (gas) CH3CH2CH2NH2 b.p. = 49C (liquid) ◼ Boiling points of amines are higher than the alkanes of similar relative molecular masses. E.g. CH3CH2CH3 (Mr = 44), b.p. = - 42C CH3CH2NH2 (Mr = 45), b.p. = 17C Reason: Amines are polar compounds and can form intermolecular hydrogen bonds. Large amount of energy is required to overcome the stronger hydrogen bonds between amine molecules. ◼ Among isomeric amines, primary amines have the highest boiling points, and tertiary amines the lowest. Reason: Tertiary amines have no N−H bond, they are unable to form intermolecular hydrogen bonds between molecules of tertiary amine. Only 1 and 2 amines can form intermolecular hydrogen bonds. WHY? Reason: For 1  and 2  amines, the H atom bonded to N can form H-bonding with the lone pair of electrons on N atom of another molecule. However, molecules of 3 amines lack a H atom bonded to the electronegative N atom, hence they can only form weaker permanent dipole–permanent dipole attractions between the molecules. ◼ For molecules with similar number of electrons, amines have lower boiling point than alcohols. Reason: Since N atom is less electronegative than O atom, the N−H bond in amines is less polar than the O−H bond in alcohols. Hence, h ydrogen bonding between amines is wea ker than the hydrogen bonding between alcohols. Compound Functional Group Mr Boiling point / °C Predominant intermolecular forces of attraction CH3CH3 Alkane 30 −89 Instantaneous dipole – induced dipole attractions CH3NH2 Amine 31 −6 Hydrogen bonding CH3OH Alcohol 32 65 Hydrogen bonding CH3 N H H N CH3 H H N H CH3 H H- bonds + - + - + + -

2025 JC2 H2 Nitrogen Compounds ©2025/ASRJC/CHEM 5 (b) Solubility (SDL) ◼ Lower alkylamines (usually amines with fewer than 5 carbon atoms) are soluble in water Reason: All amines (1, 2, 3) can form hydrogen bonds with water molecules. hydrogen bonds Tertiary amines, though they do not contain a H atom bonded to a N atom , can form hydrogen bonds with water as well (as shown in the diagram below). O H H + N R' R'' R''' − hydrogen bonds ◼ However, solubility in water decreases as molecular mass increases. E.g. Phenylamine has limited solubility in water. Reason: As molecular mass increases due to