6.2.2 Amino Acids And Chirality

Question 1

what is the simplist amino acid

Answer 1

glycine

NH2-CH2-CO2H

Question 2

general structure of an alpha amino acid

Answer 2

NH2–CH–CO2H
|
R

r group varies depending on the amino acid
alpha means NH2 and COOH are joined to the same carbon

Question 3

Zwitterions

Answer 3

no charge form of an amino acid never occurs

amino acid exists as a dipolar zwitterion

Question 4

structure of a zwitterion

Answer 4

R
             |
H3N+--C--CO2-
             |
            H

Question 5

state of amino acids

Answer 5

solids usually

Question 6

why do amino acids have high melting and boiling points

Answer 6

ionic interaction between zwitterions

Question 7

when does an amino acid exist as a zwitterion

Answer 7

at a pH value called the isoelectric point

Question 8

if the R group contains an acidic or a basic group how will this change the isoelectric point

Answer 8

the pH will be different
isoelectric point will be different
amine group in R group may make pH> 10
carboxylic acid group in R group may make pH < 3

Question 9

what is an acidic group

Answer 9

carboxylic acid group

Question 10

what is a basic group

Answer 10

amine group NH2

Question 11

Amine group on an R group

Answer 11

May make the isoelectric point be pH> 10

Question 12

Carboxylic acid group on an R group

Answer 12

May make the isoelectric point be pH< 3

Question 13

Species in alkaline solution (high pH)

Answer 13

R
           |
H2N- C- CO2-
           |
          H

Question 14

Species in neutral solution

Answer 14

R
             |
H3N+- C- CO2-
             |
            H

Question 15

Species in acidic solution (low pH)

Answer 15

R
             |
H3N+- C- CO2H
             |
            H

Question 16

What will the carboxylic acid groups or amine groups do when added to the r group

Answer 16

Will also react and change form in alkaline and acid conditions

Question 17

Reactions of amino acids

Answer 17

Carboxylic acid and amine groups can undergo the usual reactions of these functional groups in earlier topics
This is the same if alpha amine ad carboxylic acid groups

Question 18

Hydrolysis of di-peptides/proteins

Answer 18

Heat with conc acid or alkali

Can be split back into their constituent amino acids

Question 19

Amides

Answer 19

Add -amide to the stem name
Secondary an tertiary amides are named differently to show the 2 or 3 carbon chains
Smaller alkyl group is proceeded by an -N which plays the same role as a number in positioning a side alkyl chain

Question 20

Whe does when does optical isomerism occur

Answer 20

In carbon compounds with 4 different groups of atoms attached to a carbon (asymmetric carbon)

Question 21

Chiral

Answer 21

Carbon atom that has four different groups attached

Question 22

What is the molecular arrangement of carbon

Answer 22

Tetrahedral

Question 23

What does the tetrahedral arrangement cause

Answer 23

2 different isomers that aren’t super possible to be formed

They are mirror images

Question 24

Chiral atoms in nature

Answer 24

Pure enantiomer

Question 25

Optical activity

Answer 25

All amino acids except glycine are chiral because there are 4 different groups around the C

Question 26

What is an enantiomer

Answer 26

2 compounds that are optical isomers of each other

Question 27

Optical isomers properties

Answer 27

Similar physical and chemical properties
They rotate plane polarised light in different directions
1 enantiomer rotates it in one direction and the other enantiomer rotates it by the same amount in the opposite direction

Question 28

Rotation of plane polarised light

Answer 28

One will rotate light clockwise

The other will rotate light anti-clockwise

Question 29

Rotating light clockwise

Answer 29

Dextrorotatory +Ive

Question 30

Rotating light anti clockwise

Answer 30

Laevorotatory -ive