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

STRUCTURE & CLASSIFICATION StructureContain the NH 2 group Classification primary (1°) amines secondary (2°) amines tertiary (3°) aminesquarternary (4°) ammonium salts Aliphaticmethylamine, ethylamine, dimethylamine Aromatic NH 2 group is attached directly to the benzene ring (phenylamine) R N : H H R H R R R + R N R R

NOMENCLATURE NomenclatureNamed after the groups surrounding the nitrogen + amine C 2 H 5 NH 2 ethylamine (CH 3 ) 2 NHdimethylamine (CH 3 ) 3 Ntrimethylamine C 6 H 5 NH 2 phenylamine (aniline)

PREPARATION Amines can be prepared from halogenoalkanes ReagentAqueous, alcoholic ammonia ConditionsReflux in aqueous, alcoholic solution under pressure Product Amine (or its salt due to a reaction with the acid produced) NucleophileAmmonia (NH 3 ) Equation C 2 H 5 Br + NH 3 (aq / alc) ——> C 2 H 5 NH 2 + HBr ( or C 2 H 5 NH 3 + Br¯ )

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

CHEMICAL REACTIONS - WEAK BASES WaterAmines which dissolve in water produce weak alkaline solutions CH 3 NH 2 (g) + H 2 O(l) CH 3 NH 3 + (aq) + OH¯(aq) AcidsAmines react with acids to produce salts. C 6 H 5 NH 2 (l) + HCl(aq) ——> C 6 H 5 NH 3 + 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 C 6 H 5 NH 3 + Cl¯(aq) + NaOH(aq) ——> C 6 H 5 NH 2 (l) + NaCl(aq) + H 2 O(l)

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

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-aminopropanoic acid

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

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

Acidic properties: with H + HOOCCH 2 NH 2 + H + ——> HOOCCH 2 NH 3 + with HClHOOCCH 2 NH 2 + HCl ——> HOOCCH 2 NH 3 + Cl¯ Basic 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

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

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¯

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?

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 ++

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?

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 +

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