CONTENTS Prior knowledge Structure and classification Nomenclature

1. AMINES • CONTENTS • Prior knowledge • Structure and classification • Nomenclature • Physical properties • Basic properties • Nucleophilic properties • Amino acids • Peptides and proteins

2. AMINES • Before you start it would be helpful to… • know the functional groups found in organic chemistry • know the arrangement of bonds around atoms • recall and explain nucleophilic substitution reactions

3. H H R R R N: R N: R N: + R NR H R R R STRUCTURE & CLASSIFICATION Structure Contain the NH2 group Classification primary (1°) amines secondary (2°) amines tertiary (3°) amines quarternary (4°) ammonium salts Aliphaticmethylamine, ethylamine, dimethylamine AromaticNH2 group is attached directly to the benzene ring (phenylamine)

4. NOMENCLATURE NomenclatureNamed after the groups surrounding the nitrogen + amine C2H5NH2ethylamine (CH3)2NH dimethylamine (CH3)3N trimethylamine C6H5NH2phenylamine (aniline)

5. PREPARATION Amines can be prepared from halogenoalkanes ReagentAqueous, alcoholic ammonia ConditionsReflux in aqueous, alcoholic solution under pressure ProductAmine (or its salt due to a reaction with the acid produced) NucleophileAmmonia (NH3) EquationC2H5Br + NH3 (aq / alc) ——> C2H5NH2 + HBr ( or C2H5NH3+Br¯ )

6. PHYSICAL PROPERTIES The LONE PAIR on the nitrogen atom in 1°, 2° and 3° amines makes them ... NUCLEOPHILES - provide a lone pair to attack an electron deficient centre

7. CHEMICAL REACTIONS - WEAK BASES Water Amines which dissolve in water produce weak alkaline solutions CH3NH2(g) + H2O(l) CH3NH3+(aq) + OH¯(aq) Acids Amines react with acids to produce salts. C6H5NH2(l) + HCl(aq) ——> C6H5NH3+Cl¯(aq)phenylammonium chloride This reaction allows one to dissolve an amine in water as its salt. Addition of aqueous sodium hydroxide liberates the free base from its salt C6H5NH3+Cl¯(aq) + NaOH(aq) ——> C6H5NH2(l) + NaCl(aq) + H2O(l)

8. R1 H H H2N C COOH H2N C COOH H2N C COOH CH3 H R2 AMINO ACIDS StructureAmino acids contain 2 functional groups amine NH2 carboxyl COOH They all have a similar structure - the identity of R1 and R2 vary

9. H H H2NCCOOH H2NCCOOH CH3 H AMINO ACIDS – OPTICAL ISOMERISM • Amino acids can exist as optical isomers • If they have different R1 and R2 groups • Optical isomers exist when a molecule • Contains an asymmetric carbon atom • Asymmetric carbon atoms have four • different atoms or groups attached • Two isomers are formed - one rotates plane • polarised light to the left, one rotates it to the right • Glycine doesn’t exhibit optical isomerism as • there are two H attached to the C atom GLYCINE 2-aminopropanoic acid

10. R1 H3N+ C COO¯ R2 AMINO ACIDS - ZWITTERIONS Zwitterion•a dipolar ion •has a plus and a minus charge in its structure (see below) •amino acids exist as zwitterions •give increased inter-molecular forces •melting and boiling points are higher

11. R1 H2N C COOH R2 AMINO ACIDS - ACID-BASE PROPERTIES •amino acids possess acidic and basic properties • this is due to the two functional groups (see above) • COOH gives acidic properties • NH2 gives basic properties • they form salts when treated with acids or alkalis.

12. AMINO ACIDS - ACID-BASE PROPERTIES Acidic properties: with H+HOOCCH2NH2 + H+ ——> HOOCCH2NH3+ with HCl HOOCCH2NH2 + HCl ——> HOOCCH2NH3+ Cl¯ Basic properties: with OH¯ HOOCCH2NH2 + OH¯ ——> ¯OOCCH2NH2 + H2O with NaOH HOOCCH2NH2 + NaOH ——> Na+ ¯OOCCH2NH2 + H2O

13. PEPTIDES - FORMATION & STRUCTURE Amino acids can join together to form peptides via an amide or peptide link 2 amino acids joined dipeptide 3 amino acids joined tripeptide many amino acids joined polypeptide a dipeptide

14. PEPTIDES - HYDROLYSIS Peptides are broken down into their constituent amino acids by hydrolysis • attack takes place at the slightly positive C of the C=O • the C-N bond is broken • hydrolysis with water is very slow • hydrolysis in alkaline/acid conditions is quicker • hydrolysis in acid/alkaline conditions (e.g. NaOH) will produce salts with HCl NH2 becomes NH3+Cl¯ H+ NH2 becomes NH3+ NaOH COOH becomes COO¯ Na+ OH¯ COOH becomes COO¯

15. H H CH3 NH C COOH H2N C CO NH C CO CH3 CH3 H PEPTIDES - HYDROLYSIS Peptides are broken down into their constituent amino acids by hydrolysis Which amino acids are formed?

16. H H CH3 NH C COOH H2N C CO NH C CO CH3 CH3 H H H CH3 H2N C COOH H2N C COOH H2N C COOH CH3 CH3 H PEPTIDES - HYDROLYSIS Peptides are broken down into their constituent amino acids by hydrolysis + +

17. H H H NH C COOH H2N C CO NH C CO CH3 CH3 H PEPTIDES - HYDROLYSIS Peptides are broken down into their constituent amino acids by hydrolysis Which amino acids are formed?

18. H H H H H NH C COOH H2N C CO NH C CO H2N C COOH H2N C COOH CH3 CH3 H CH3 H PEPTIDES - HYDROLYSIS Peptides are broken down into their constituent amino acids by hydrolysis 2 x +

19. PROTEINS • are polypeptides with high molecular masses • chains can be lined up with each other • the C=O and N-H bonds are polar due to a difference in electronegativity • hydrogen bonding exists between chains dotted lines ---------- represent hydrogen bonding