6.2.2: Amino acids, amides and chirality

Question 1

What are the two functional groups of amino acids?

Answer 1

NH2 and COOH (amine and carboxylic acid)

Question 2

Draw a general formula for α-amino acids.

Answer 2

NH2
R-C-COOH
H

Question 3

Are α-amino acids chiral? Why?

Answer 3

Yes, one carbon has 4 different substituents.

Except glycine, where R = H.

Question 4

Define a zwitterion.

Answer 4

Ions which have both a permanent positive and negative charge, but are neutral overall.

Question 5

How do zwitterions occur in amino acids?

Answer 5

COOH is deprotonated → COO_

NH2 is protonated → NH3+

Question 6

What happens to amino acids in acidic conditions?

Answer 6

Gains a proton on NH2 group

Question 7

What happens to amino acids in alkaline conditions?

Answer 7

Loses a proton from COOH group

Question 8

What is the peptide linkage?

Answer 8

-CONH (C=O, H-N)

Question 9

What property must a carbon atom have for the
molecule to display optical isomerism about that
carbon atom?

Answer 9

4 different substituents attached to one carbon atom

Question 10

What are the similarities and differences between

two optical isomers?

Answer 10

Same atoms and bonds, but they are non superimposable mirror images of one another. NOT IDENTICAL in chemical properties necessarily.
Differ in the way they rotate plane polarised light - rotate
plane of polarisation by the same angle but in different
directions

Question 11

What word is used to describe optically active

molecules?

Answer 11

chiral

Question 12

Give two examples of chiral molecules

Answer 12

All alpha amino acids, except glycine.

Lactic acid / 2-hydroxypropanoic acid