CONTENTS

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
STRUCTURE CLASSIFICATION
Structure Contain the NH2 group Classification
primary (1) amines secondary
(2) amines tertiary (3)
amines quarternary (4) ammonium
salts Aliphatic methylamine, ethylamine,
dimethylamine Aromatic NH2 group is attached
directly to the benzene ring (phenylamine)
4
NOMENCLATURE
Nomenclature Named after the groups surrounding
the nitrogen amine C2H5NH2 ethylamine
(CH3)2NH dimethylamine (CH3)3N trimethylamin
e C6H5NH2 phenylamine (aniline)
5
PREPARATION
Amines can be prepared from halogenoalkanes Reag
ent Aqueous, alcoholic ammonia Conditions Reflux
in aqueous, alcoholic solution under
pressure Product Amine (or its salt due to a
reaction with the acid produced) Nucleophile Ammo
nia (NH3) Equation C2H5Br NH3 (aq / alc)
gt C2H5NH2 HBr ( or C2H5NH3Br )
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 Am
ines react with acids to produce
salts. C6H5NH2(l) HCl(aq) gt
C6H5NH3Cl(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 C6H5NH3Cl(aq) NaOH(aq)
gt C6H5NH2(l) NaCl(aq) H2O(l)
8
AMINO ACIDS
Structure Amino acids contain 2 functional
groups amine NH2
carboxyl COOH They all have a
similar structure - the identity of R1 and R2 vary
9
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 doesnt exhibit optical isomerism as
• there are two H attached to the C atom

GLYCINE 2-aminopropanoic acid
10
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
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
gt HOOCCH2NH3 with HCl HOOCCH2NH2
HCl gt HOOCCH2NH3 Cl Basic
properties with OH HOOCCH2NH2 OH gt
OOCCH2NH2 H2O with NaOH HOOCCH2NH2
NaOH gt 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 CO
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
NH3Cl H NH2 becomes NH3
NaOH COOH becomes COO Na
OH COOH becomes COO
15
PEPTIDES - HYDROLYSIS
Peptides are broken down into their constituent
amino acids by hydrolysis
Which amino acids are formed?
16
PEPTIDES - HYDROLYSIS
Peptides are broken down into their constituent
amino acids by hydrolysis


17
PEPTIDES - HYDROLYSIS
Peptides are broken down into their constituent
amino acids by hydrolysis
Which amino acids are formed?
18
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
CO and N-H bonds are polar due to a difference
in electronegativity hydrogen bonding exists
between chains dotted lines ----------
represent hydrogen bonding