The Amides

1
The Amides
2

• Carboxylic acids can be converted directly to the
  corresponding amides by the reaction of an acid
  with the appropriate amine.
• The amine used in this reaction can be ammonia, a
  primary amine, or a secondary amine, depending on
  the degree of nitrogen substitution expected.

3
Preparation of Amides(C Method)
While this is not the best method of preparing
amides, it has the advantage of being simple. It
also serves to introduce the amides as a class of
compounds.
4
Preparation of Amides(A Method)
5

• REMEMBER The previous image neglects to account
  for the H-Cl produced in the reaction.
• In each of the previous reactions, two
  equivalents of amine are required -- one to act
  as nucleophile and the second to act as a base.
  The second equivalent of amine reacts with the
  H-Cl to form the corresponding amine
  hydrochloride.

6
Peptides and Proteins
7
Amino acids have the general structure

• The correct Fischer projection for
  naturally-occurring amino acids is shown here.
• The R group is variable.

8

• As can be seen, the amino acids possess both
  functional groups required to form an amide.
  Each amino acid is both a carboxylic acid and an
  amine simultaneously.
• Therefore, it should be possible to link amino
  acids together through the formation of amides.

9
Peptide bond(an amide linkage)
10
Peptides

• When amino acids are linked together by amide
  linkages (biochemists call these peptide
  bonds), the resulting molecule is called a
  peptide.
• A peptide is a polymer formed from individual
  amino acid units.

11
Peptides

• Peptides are named according to the number of
  amino acids that are linked
• dipeptide two amino acids
• tripeptide three amino acids
• tetrapeptide four amino acids
• etc.
• The term oligopeptide refers an amino acid
  polymer with a moderate number of repeating amino
  acid units.

12
Peptides and Proteins

• When a peptide grows to a length of about 70
  amino acid units (molecular weight
  approximately 10,000), the molecule begins to
  coil onto itself and assume a particular
  secondary structure.
• At this point, we no longer refer to the molecule
  as a peptide we begin to call it a protein.

13
alpha-Helix
14
Chateau de Chambord
15
Chambord Double Staircase by Leonardo DaVinci
16
Other Amide Polymers
NYLON!!!
17
Hydrolysis of Amides

• The most important reaction of amides is
  hydrolysis.
• The products of amide hydrolysis are the
  carboxylic acid and the amine.

18
Hydrolysis of Amides
This reaction can also be run under basic
conditions.
19
Hydrolysis of Amides

• In living organisms, the hydrolysis of peptides
  is accomplished through catalysis by enzymes.
• The enzyme-catalyzed hydrolysis of peptides and
  proteins is what happens to protein when we eat
  it.
• The protein is hydrolyzed into individual amino
  acids, which are then used to build new proteins.

20
Example
21
Reduction of Amides

• If either R1 or R2 is hydrogen in the amide, the
  corresponding R groups will be hydrogen in the
  amine product. Notice that the carbonyl group is
  reduced to a methylene group.
• NaBH4 cannot reduce amides

22
Examples
23
Nitriles
24
Formation of Nitriles
This is an SN2 reaction. It works best with
primary alkyl halides.
25
Hydrolysis of Nitriles
The reaction can be conducted in either acidic or
basic solution.
26
Example
27
Example
28
Base-Promoted Hydrolysis of a Nitrile (Part One)
29
Base-Promoted Hydrolysis of a Nitrile (Part Two)
30
Acid-catalyzed Hydrolysis of a Nitrile (Part One)
31
Acid-catalyzed Hydrolysis of a Nitrile (Part Two)
32
Reduction of Nitriles
NaBH4 does not reduce nitriles.
33
Also
CAUTION!!!
34
Example
35
Example
36
Reduction of a Nitrile to an Aldehyde