AMIDES AND AMINO AMIDES AND AMINO ACIDSACIDS
AMIDESAMIDES
Structure derivatives of carboxylic acids
amide group is -CONH2
NomenclatureWhite crystalline solids named from the corresponding acid(remove oic acid, add amide)
CH3CONH2 ethanamide (acetamide)
CH3CONHC2H5 N - ethyl ethanamide - the N tells you the
substituent is on
the nitrogen
Nylons are examples of polyamides
Preparation Acyl chloride + ammonia
CH3COCl + NH3 ——> CH3CONH2 + HCl ethanoyl chloride ethanamide
Physical propertiesPhysical properties The N-H bond is polar and results in The N-H bond is polar and results in
extensive intermolecular hydrogen extensive intermolecular hydrogen bonding.bonding.
The melting and boiling points of The melting and boiling points of amides are relatively high.amides are relatively high.
Apart from methanamide (a liquid) all Apart from methanamide (a liquid) all amides are white crystalline solids.amides are white crystalline solids.
They are all very soluble in water.They are all very soluble in water.
AMIDES - AMIDES - CHEMICAL PROPERTIESCHEMICAL PROPERTIES
Hydrolysisgeneral reaction CH3CONH2 + H2O ——> CH3COOH + NH3
acidic soln. CH3CONH2 + H2O + HCl ——> CH3COOH + NH4Clalkaline soln. CH3CONH2 + NaOH ——> CH3COONa + NH3
Identification Warming an amide with dilute sodium hydroxide solution andtesting for the evolution of ammonia using moist red litmus
paperis used as a simple test for amides.
ReductionReduced to primary amines: CH3CONH2 + 4[H] ——> CH3CH2NH2 + H2O(LiAlH4 in ethoxyethane is used as the reducing agent)
Polyamides – condensation Polyamides – condensation polymers 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-Hexanedioic acid was condensed with 1,6-
diaminohexane to produce nylon-66.diaminohexane to produce nylon-66. In the 1960s another polyamide known as “Kevlar” was In the 1960s another polyamide known as “Kevlar” was
developed by the same laboratories.developed by the same laboratories. Kevlar has high temperature resistance and low thermal Kevlar has high temperature resistance and low thermal
conductivity, high tensile strength, doesn’t shrink in the conductivity, high tensile strength, doesn’t shrink in the wash, is flame, chemical and cutting resistant. wash, is flame, chemical and cutting resistant.
Applications so far include – bullet proof vests vehicle Applications so far include – bullet proof vests vehicle hoses, structural parts in aircraft, space shuttles and hoses, structural parts in aircraft, space shuttles and boat, protective clothing, ropes etcboat, protective clothing, ropes etc
AMINO ACIDSAMINO 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
H2N C COOH
H
H
H2N C COOH
CH3
H
H2N C COOH
R2
R1
AMINO ACIDS – AMINO ACIDS – OPTICAL ISOMERISMOPTICAL ISOMERISM
Amino acids can exist as optical isomersIf they have different R1 and R2 groups
Optical isomers exist when a moleculeContains an asymmetric carbon atom
Asymmetric carbon atoms have fourdifferent atoms or groups attached
Two isomers are formed - one rotates planepolarised light to the left, one rotates it to the right
Glycine doesn’t exhibit optical isomerism asthere are two H attached to the C atom
H2N C COOH
CH3
H
H2N C COOH
H
H
GLYCINE2-aminoethanoic acid
ALANINE2-aminopropanoic acid
AMINO ACIDS - AMINO ACIDS - ZWITTERIONSZWITTERIONS
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
H3N+ C COO¯
R2
R1
• 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.
H2N C COOH
R2
R1
AMINO ACIDS - AMINO ACIDS - ACID-BASE PROPERTIESACID-BASE PROPERTIES
AMINO ACIDS - AMINO ACIDS - ACID-BASE PROPERTIESACID-BASE PROPERTIES
Basic properties:
with H+ HOOCCH2NH2 + H+ ——> HOOCCH2NH3+
with HCl HOOCCH2NH2 + HCl ——> HOOCCH2NH3+ Cl¯
Acidic properties:
with OH¯ HOOCCH2NH2 + OH¯ ——> ¯OOCCH2NH2 + H2O
with NaOH HOOCCH2NH2 + NaOH ——> Na+ ¯OOCCH2NH2 + H2O
PEPTIDES - PEPTIDES - FORMATION & STRUCTUREFORMATION & 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
PEPTIDES - PEPTIDES - HYDROLYSISHYDROLYSIS
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 HCl NH2 becomes NH3+Cl¯
H+ NH2 becomes NH3+
NaOH COOH becomes COO¯ Na+
OH¯ COOH becomes COO¯
PEPTIDES - PEPTIDES - HYDROLYSISHYDROLYSIS
Peptides are broken down into their constituent amino acids by hydrolysis
H2N C CO
CH3
H
NH C CO
H
H
NH C COOH
CH3
CH3
Which amino acids are formed?
PEPTIDES - PEPTIDES - HYDROLYSISHYDROLYSIS
Peptides are broken down into their constituent amino acids by hydrolysis
H2N C CO
CH3
H
NH C CO
H
H
NH C COOH
CH3
CH3
CH3
H
H2N C COOH
H
H
H2N C COOH
CH3
CH3
H2N C COOH++
H2N C CO
CH3
H
NH C CO
H
H
NH C COOH
H
CH3
PEPTIDES - PEPTIDES - HYDROLYSISHYDROLYSIS
Peptides are broken down into their constituent amino acids by hydrolysis
Which amino acids are formed?
H2N C CO
CH3
H
NH C CO
H
H
NH C COOH
H
CH3
PEPTIDES - PEPTIDES - HYDROLYSISHYDROLYSIS
Peptides are broken down into their constituent amino acids by hydrolysis
CH3
H
H2N C COOH
H
H
H2N C COOH2 x +
PROTEINSPROTEINS
• 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
THE ENDTHE END