1. AMIDES AND AMINO ACIDS AMIDES AND AMINO ACIDS

2. AMIDES Structurederivatives of carboxylic acids amide group is -CONH 2 NomenclatureWhite crystalline solids named from the corresponding acid (remove oic acid, add amide) CH 3 CONH 2 ethanamide (acetamide) CH 3 CONHC 2 H 5 N - ethyl ethanamide -the N tells you the substituent is on the nitrogen Nylons are examples of polyamides PreparationAcyl chloride + ammonia CH 3 COCl + NH 3 ——> CH 3 CONH 2 + HCl ethanoyl chloride ethanamide

3. Physical properties The N-H bond is polar and results in extensive intermolecular hydrogen bonding. The N-H bond is polar and results in extensive intermolecular hydrogen bonding. The melting and boiling points of amides are relatively high. The melting and boiling points of amides are relatively high. Apart from methanamide (a liquid) all amides are white crystalline solids. Apart from methanamide (a liquid) all amides are white crystalline solids. They are all very soluble in water. They are all very soluble in water.

4. AMIDES - CHEMICAL PROPERTIES Hydrolysis general reaction CH 3 CONH 2 + H 2 O ——> CH 3 COOH + NH 3 acidic soln. CH 3 CONH 2 + H 2 O + HCl ——> CH 3 COOH + NH 4 Cl alkaline soln. CH 3 CONH 2 + NaOH ——> CH 3 COONa + NH 3 IdentificationWarming an amide with dilute sodium hydroxide solution and testing for the evolution of ammonia using moist red litmus paper is used as a simple test for amides. Reduction Reduced to primary amines: CH 3 CONH 2 + 4[H] ——> CH 3 CH 2 NH 2 + H 2 O (LiAlH 4 in ethoxyethane is used as the reducing agent)

5. Polyamides – condensation polymers The first polyamide (Nylon) was developed in the 1940s. The first polyamide (Nylon) was developed in the 1940s. Hexanedioic acid was condensed with 1,6- diaminohexane to produce nylon-66. Hexanedioic acid was condensed with 1,6- diaminohexane to produce nylon-66. In the 1960s another polyamide known as “Kevlar” was developed by the same laboratories. In the 1960s another polyamide known as “Kevlar” was developed by the same laboratories. Kevlar has high temperature resistance and low thermal conductivity, high tensile strength, doesn’t shrink in the wash, is flame, chemical and cutting resistant. Kevlar has high temperature resistance and low thermal conductivity, high tensile strength, doesn’t shrink in the wash, is flame, chemical and cutting resistant. Applications so far include – bullet proof vests vehicle hoses, structural parts in aircraft, space shuttles and boat, protective clothing, ropes etc Applications so far include – bullet proof vests vehicle hoses, structural parts in aircraft, space shuttles and boat, protective clothing, ropes etc

6. AMINO ACIDS Structure Amino acids contain 2 functional groups amine NH 2 carboxyl COOH They all have a similar structure - the identity of R 1 and R 2 vary H 2 N C COOH H H CH 3 H H 2 N C COOH R2R2 R 1

7. AMINO ACIDS – OPTICAL ISOMERISM Amino acids can exist as optical isomers If they have different R 1 and R 2 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 H 2 N C COOH CH 3 H H 2 N C COOH H H GLYCINE 2-aminoethanoic acid ALANINE 2-aminopropanoic acid

8. 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 H 3 N + C COO¯ R2R2 R1R1

9. amino acids possess acidic and basic properties this is due to the two functional groups (see above) COOH gives acidic properties NH 2 gives basic properties they form salts when treated with acids or alkalis. H 2 N C COOH R2R2 R1R1 AMINO ACIDS - ACID-BASE PROPERTIES

10. Basic properties: with H + HOOCCH 2 NH 2 + H + ——> HOOCCH 2 NH 3 + with HClHOOCCH 2 NH 2 + HCl ——> HOOCCH 2 NH 3 + Cl¯ Acidic properties: with OH¯HOOCCH 2 NH 2 + OH¯ ——> ¯OOCCH 2 NH 2 + H 2 O with NaOH HOOCCH 2 NH 2 + NaOH ——> Na+ ¯OOCCH 2 NH 2 + H 2 O

11. PEPTIDES - FORMATION & STRUCTURE Amino acids can join together to form peptides via an amide or peptide link 2 amino acids joineddipeptide 3 amino acids joinedtripeptide many amino acids joinedpolypeptide a dipeptide

12. 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 HClNH 2 becomes NH 3 + Cl¯ H + NH 2 becomes NH 3 + NaOHCOOHbecomes COO¯ Na + OH¯COOHbecomes COO¯

13. PEPTIDES - HYDROLYSIS Peptides are broken down into their constituent amino acids by hydrolysis H 2 N C CO CH 3 H NH C CO H H NH C COOH CH 3 Which amino acids are formed?

14. PEPTIDES - HYDROLYSIS Peptides are broken down into their constituent amino acids by hydrolysis H 2 N C CO CH 3 H NH C CO H H NH C COOH CH 3 H H 2 N C COOH H H CH 3 H 2 N C COOH ++

15. H 2 N C CO CH 3 H NH C CO H H NH C COOH H CH 3 PEPTIDES - HYDROLYSIS Peptides are broken down into their constituent amino acids by hydrolysis Which amino acids are formed?

16. H 2 N C CO CH 3 H NH C CO H H NH C COOH H CH 3 PEPTIDES - HYDROLYSIS Peptides are broken down into their constituent amino acids by hydrolysis CH 3 H H 2 N C COOH H H 2 x +

17. 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

18. THE END