Amino Acids and Chirality

Question 0

What is the pH value of an amino acid as a zwitter ion called?

Answer 0

Isoelectric point

Question 1

What is the general formula of an alpha amino acid?

Answer 1

RCH(NH2)COOH

Question 2

What kind of ion does an amino acid form?

Answer 2

Zwitter ion

Question 3

How do isoelectric points vary?

Answer 3

With different R groups

Question 4

What are the acid-base properties of alpha amino acids at a pH more acidic than the isoelectric point?

Answer 4

• the amino acid behaves as a base and accepts a proton from the acid
• forms a positively charged ion

Question 5

What are the acid-base properties of alpha amino acids at a pH more alkaline than the isoelectric point?

Answer 5

• the amino acid behaves as an acid and donates a proton to the base
• the amino acid forms a negatively charged ion

Question 6

How is a peptide linkage between alpha amino acids formed?

Answer 6

Through a condensation reaction

• water is lost
• leads to condensation polymerisation which forms proteins/polypeptides

Question 7

Describe the acid hydrolysis of polypeptides

Answer 7

• using aqueous acid
• water molecules needed to break peptide links to form amino acids
• amino acids formed are positively charged because of H+ ions in the acid
• heated under reflux with 6moldm^-3 for 24 hours.

Question 8

Describe the alkaline hydrolysis of polypeptides

Answer 8

• solution of alkali (NaOH) used at above 100*C

- polypeptide is broken down into amino acids in form of sodium salts

Question 9

What are optical isomers?

Answer 9

Non-superimposable mirror images about an organic chiral centre. Four different groups are attached to the carbon atom.

Question 10

What are two different types of stereoisomerism?

Answer 10

Optical isomerism

E/Z isomerism

Question 11

Definition of condensation polymerisation

Answer 11

The joining of two monomers with the elimination of a small molecule, such as water or HCl

Question 12

How are polyesters formed?

Answer 12

-monomer units are bonded together by ester linkages
-the monomers have a carboxyl group and a hydroxyl group
Two types of polyesters:
1. One monomer is a dicarboxylic acid, the other is a diol
2. Both monomers contain both carboxyl and hydroxyl groups

Question 13

How are polyamides formed?

Answer 13

-monomers are bonded together by amide linkages.
-the monomers have a carboxyl group and an amide group
Two types of polyamides:
1. One monomer is a dicarboxylic acid, the other is a diamine
2. Both monomers contain both carboxyl and amide groups

Question 14

Difference between condensation and addition polymerisation

Answer 14

• addition polymers are made from only one type of monomer, there is no product other than the monomer.
• condensation polymers are made from joining two monomers with the elimination of a small molecule. The monomers must have two functional groups in the structure.

Question 15

What are the uses of polyesters and polyamides?

Answer 15

Used in fibres for clothing

• the bonds are strong
• long chains of polyamides are held together by hydrogen bonded which are easily broken and reformed making nylon fibres elastic.
• for polyesters, cross-linking through dipole-dipole bonding occurs making fibres elastic.

Question 16

Describe the acid hydrolysis of polyesters

Answer 16

• hydrolysed using hot, aqueous acid such as HCl
• the monomer units of the polyester are produced
• reaction is slower than with aqueous alkali

Question 17

Describe the base hydrolysis of polyesters

Answer 17

-hydrolysed by hot aqueous alkalis, like NaOH
-ester linkage hydrolysed to
•sodium salt of a carboxylic acid
•hydroxyl group

Question 18

Describe the acid hydrolysis of polyamides

Answer 18

• hydrolysed by hot aqueous acid such as HCl

- dicarboxylic acid and an ammonium salt of the diamine are produced

Question 19

Describe the base hydrolysis of polyamides

Answer 19

• hydrolysed with hot aqueous alkali, such as NaOH

- sodium salt of the dicarboxylic acid and the diamine are formed