amides and amino acids amides and amino acids. amides structurederivatives of carboxylic acids amide...

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¯



H2N C CO

CH3

H

NH C CO

H

H

NH C COOH

CH3

CH3

Which amino acids are formed?



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



Which amino acids are formed?

H2N C CO

CH3

H

NH C CO

H

H

NH C COOH

H

CH3



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

amides and amino acids amides and amino acids. amides structurederivatives of carboxylic acids amide...

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