Organic bases are Amines
Amines ( -NH 2 ) are derivatives of ammonia
R
H N H
H
N H
H
Primary (1o) Amine
Ammonia
R N R
R
R N H
R
o
Secondary (2 ) Amine
Tertiary (3 o) Amine
Amines -- Systematic Nomenclature
Name amines like alcohols.
Replace “e” of alkane with amine
Note: Amines (amino prefix) have lower priority than alcohols or acids.
Trivial names are like those of ethers but the final name is amine
H2 N
NH2
1,3-propanediamine
o
Naming 1 amines
IUPAC and Common Names
o
Naming 2 amines
P Smaller groups on the amine N are located
with N
P Common names label organic groups in front
of amine
H 3 CH2C
CH3
N
H
o
Naming 3 amines
As a prefix, the -NH 2 group is called amino
Chemistry of Amines
R
NH2
R1
Aliphatic amines…
R2
N
H
N
H 2N
N
N
N
N
R2
R3
O
Heterocyclic amines…
R1
N
Caffeine
O
N
H
Serotonin
OH
Seratonin
Naturally Occurring Amines -Examples
H
Examples of
Alkaloids
N
CH 3
CH3
N
O
N
Examples of
Heterocycles
OCH 3
(S)-(-)-Nicotine
O
Cocaine
O
Some Common Amines
1,4-butanediamine
NH2
H2N
Putrescine
(found in decaying meat)
NH2
Both upper amines are 1o
N
Amphetamine
(dangerous stimulant)
N
This amine is 3o
H
Piperidine
This amine is 2o
Triethylamine
PHYSICAL PROPERTIES
Boiling point
Boiling points increase with molecular mass
Amines have higher boiling
points than corresponding
alkanes because of their
intermolecular hydrogen bonding
Solubility
Lower mass compounds are
soluble in water due to hydrogen
bonding with the solvent.
Solubility decreases as the
molecules get heavier.
Soluble in organic solvents.
CHEMICAL REACTIONS - Amines areWEAK BASES
Water
Amines which dissolve in water produce weak alkaline solutions
CH3NH2(g)
Acids
+
H 2O(l)
CH 3NH3+(aq)
+
O
H
a
q()
Amines react with acids to produce salts.
C 6 H 5 NH 2 (l)
+
HCl(aq) ——> C 6 H 5 NH 3 + Cl
Amine salts are water soluble.
a(q)
phenylammonium chloride
PREPARATION OF AMINES
Amines can be prepared from Alkyl halides
Equation
C2H5Br + NH3 (aq)
——> C2H5NH2 + HBr
Ammonia (NH 3)
SUBSTITUTION
HALOALKANES
Primary Amines can react with
.
haloalkanes to produce secondary amines
C 2 H 5 NH 2 + C 2 H 5 Br
——> HBr + (C 2 H 5 )2 NH
diethylamine, 2E amine
Secondary Amines can react with
haloalkanes to produce tertiary amines
(C 2 H 5 )2 NH + C 2 H 5 Br ——> HBr + (C 2 H 5 )3 N
triethylamine, 3E amine
Synthesis of an amine from an alkyl halide
AMINO ACIDS
Structure
Amino acids contain 2 functional groups
amine
NH 2
carboxyl
R1
H2 N
COOH
C
COOH
R2
They all have a similar structure - the identity of R 1 and R 2 vary
H
H2 N
C
H
H
COOH
H2 N
C
CH3
COOH
AMINO ACIDS: OPTICAL ISOMERISM
P Optical isomers (enantiomers) have 4 different
groups attached to a carbon atom
P Optical isomers rotate plane polarised light in
opposite directions
P 2-aminoethanoic acid (glycine) doesn’t have optical
isomers
P 2-aminopropanoic acid (alanine) has optical
isomers
H
H
H2 N
C
COOH
H
GLYCINE
2-aminoethanoic acid
H2 N
C
COOH
CH3
ALANINE
2-aminopropanoic acid
AMINO ACIDS: OPTICAL ISOMERISM
P Optical isomers are like left and right hands
P Optical isomers are non-superimposable mirror
images
P Chiral molecules have optical isomers
P Switching any 2 groups on the carbon changes the
isomer
Properties of Enantiomers
Enantiomers have identical:
P Melting points
P Boiling points
P Solubility in solvents
P Reactions with achiral molecules
Properties of Enantiomers
Enantiomers have different:
P Interactions with chiral molecules
P Rates of reactions with chiral molecules
P Directions of rotation of polarized light (equal
but opposite direction
P 3-D shapes
Enantiomers may have different odours
Caraway
Spearmint
AMINO ACIDS - ACID -BASE PROPERTIES
• amino acids possess acidic and basic properties
• this is due to the two functional groups
• COOH gives acidic properties
• NH2 gives basic properties
• they form salts when treated with acids or bases.
R1
H2 N
C
R2
COOH
AMINO ACIDS - ACID -BASE PROPERTIES
Basic properties:
with H+
HOOCCH2NH2
+ H+
——>
HOOCCH2NH3+
with HCl
HOOCCH2NH2
+ HCl
——>
HOOCCH2NH3+ Cl
Acidic properties:
w
OiH
th
HOOCCH2NH2
+OH
——>
with NaOH
HOOCCH2NH2 + NaOH ——N
>a+
OOCCH2NH2 + H2O
OOCCH2NH2 + H2O
AMIDES or 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
AMIDES
Structure
derivatives of carboxylic acids
amide group is
Nomenclature
-CONH 2
White crystalline solids named from the corresponding acid
(remove oic acid, add amide)
CH 3 CONH 2
ethanamide (acetamide)
C 2 H 5 CONHC 6 H 5
N - phenyl propanamide -
the N tells you the
substituent is on
the nitrogen
Proteins and Nylons are examples of polyamides
PEPTIDES - HYDROLYSIS
Peptides are broken down into their constituent amino acids by hydrolysis
H
H2 N
H
C
CO NH
CH3
C
H
CH3
CO NH
C
CH3
Which amino acids are formed?
COOH
PEPTIDES - HYDROLYSIS
Peptides are broken down into their constituent amino acids by hydrolysis
H
H2 N
C
H
CO NH
CH3
C
CH3
CO NH
C
COOH
CH3
H
H
H
H2 N
C
CH3
COOH
+
H2 N
C
H
CH3
COOH
+
H2N
C
CH3
COOH
PEPTIDES - HYDROLYSIS
Peptides are broken down into their constituent amino acids by hydrolysis
H
H2 N
H
C
CO NH
CH3
C
H
H
CO NH
C
CH3
Which amino acids are formed?
COOH
PEPTIDES - HYDROLYSIS
Peptides are broken down into their constituent amino acids by hydrolysis
H
H2 N
C
H
CO NH
CH3
H
CO NH
C
H2N
C
CH3
COOH
CH3
H
H
H
2x
C
COOH
+
H2 N
C
H
COOH
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
Interpeptide interactions, especially
hydrogen bonds, lead to complex
structures and folding patterns.
Polyamides (Nylons)
n Heating a diamine with a diacid produces a
polyamide called Nylon ®
n Nylon 66® is from adipic acid and hexamethylenediamine at 280EC
Adapted from JONATHAN HOPTON & KNOCKHARDY PUBLISHING
Based on McMurry's Organic Chemistry, 6th edition