27.2 Amino Acids, Amides & Chirality

Question 1

What is an amino acid?

Answer 1

Organic compound

containing both amine & carboxyl groups

general formula RCH(NH₂)COOH

Question 2

Describe the reactions of Amino Acids in relation to its functional groups:

Answer 2

Amino acids react similarly to carboxylic acids & amines,

since they have both carboxyl & amine functional groups

Question 3

What is an alpha amino acid?

Answer 3

amino acid

in which same carbon is attached to amine & carboxyl group

Question 4

Amino acid + Acid ⟶

Answer 4

ammonium salt

(H⁺ from acid forms dative covalent bond with :N ⟶ NH₃⁺, then forms ionic bond with Cl^-)

Question 5

Amino Acid + Alkali ⟶

Answer 5

Salt + Water

(metal from alkali substitutes H in carboxyl, leaving salt + H⁺ + OH^-)

Question 6

Amino acid + Alcohol ⟶

Answer 6

Ester + Water (esterification)

Concentrated H₂SO₄ catalyst

(acidic conditions protonate amine group)

Question 7

Amino acid + Alcohol ⟶ Ester + Water

What condition(s) is/are required for this reaction?

Answer 7

concentrated H₂SO₄ catalyst

Question 8

What is an amide?

Answer 8

Molecule where nitrogen is bonded to carbonyl group

formed from acyl chloride + amine/ammonia

Question 9

What happens to the amine group during esterification of an amino acid?

Answer 9

protonated ⟶ NH₃⁺

(because of acidic conditions)

Question 10

How is an amide made?

Answer 10

Acyl chloride + Ammonia

Question 11

Acyl chloride + Ammonia ⟶

Answer 11

Amide + HCl

Question 12

Draw the general structure of a primary amide:

Answer 12

Question 13

Draw the general structure of a secondary amide:

Answer 13

Question 14

Draw the general structure of a tertiary amide:

Answer 14

Question 15

Amino Acids, Amides & Chirality

Which type of molecules show optical isomerism?

Answer 15

molecules with chiral carbons

Question 16

What is a chiral carbon?

Answer 16

carbon with 4 different groups attached

Question 17

A molecule has 2 chiral carbons. How many optical isomers does it have?

Answer 17

4

(1 pair for each chiral carbon)

Question 18

Can carbons with a double bond form optical isomers?

Answer 18

No

because does not have 4 different groups attached

Question 19

What is an enantiomer?

Answer 19

molecules which are non-superimposable mirror images of each other,

AKA optical isomers

Question 20

What is a zwitterion?

Answer 20

ion with both positive & negative charge

Question 21

What is the isoelectric point of an amino acid?

Answer 21

pH at which it is present as a zwitterion

unique to each type of amino acid

Question 22

Describe the state of an amino acid molecule at it’s isoelectric point:

Answer 22

H⁺ from carboxyl accepted by amine group

(by forming dative covalent bond :N)

amino acid present as zwitterion, due to NH₃⁺ & COO^-

Question 23

Describe the state of an amino acid above it’s isoelectric point:

Answer 23

Lower [H⁺_(aq)], so NH₃⁺ loses H⁺

∴ amino acid present as anion due to COO^-

Question 24

Describe the state of an amino acid below it’s isoelectric point:

Answer 24

Greater [H⁺_(aq)], so H⁺ in solution protonates carboxyl group

∴ amino acid present as cation due to NH₃⁺