Topic 9 Alcohols & Carbohydrates

Question 1

Arrange the following in order of increasing expected pKa
value (i.e. from the most acidic to the most basic):
(1) propanol
(2) tert-butanol
(3) glutamate (side chain)
(4) histidine (side chain)

A. 1 < 3 < 2 < 4
B. 2 < 1 < 4 < 3
C. 3 < 4 < 1 < 2
D. 3 < 4 < 2 < 1
E. 1 < 2 < 3 < 4

Answer 1

C. 3 < 4 < 1 < 2

Question 2

Arrange the following functional groups in order of increasing
expected pKa value (i.e. from the most acidic to the most basic):
(1) ethanol
(2) acetic acid
(3) ethane
(4) phenol

A. 1 < 3 < 2 < 4
B. 2 < 1 < 4 < 3
C. 2 < 4 < 1 < 3
D. 3 < 2 < 4 < 1
E. 1 < 2 < 3 < 4

Answer 2

C. 2 < 4 < 1 < 3

Question 3

Which of the following statements about sugars is FALSE?
A. Six-membered (pyranose) ring forms of sugars are
usually energetically preferred over 5-membered
(furanose) forms
B. Pyranose and furanose forms interconvert via
formation of the straight chain form.
C. Pyranose forms are formed by nucleophilic attack
of the C5 hydroxyl group with the carbonyl carbon.
D. Furanose forms are formed by nucleophilic attack
of the C6 hydroxyl group with the carbonyl carbon.
E. Chair conformations of pyranose rings are
energetically more stable than boat
conformations

Answer 3

D. Furanose forms are formed by nucleophilic attack

of the C6 hydroxyl group with the carbonyl carbon

Question 4

Draw the mechanism by which a C-6 sugar interconverts between straight-chain and cyclic forms. Sketch the conformations the cyclic forms can adopt and indicate which are the most energetically favoured.

Answer 4

The 6-membered ring is energetically preferred, because it has less torsional strain

Question 5

Using an annotated diagram, illustrate the differences between a1,4, β1,4 and a1,6 glycosidic bonds

Answer 5

a1,4 = linear, helical coils
a1,6 = leads to branches
b1,6= parallel rows

Question 6

Draw the aldose, pyranose and furanose forms of D-glucose, and comment on their relative abundances and stabilities in solution.

Answer 6

The 6-membered ring is energetically preferred, because it has less torsional strain
Pyranose = >99.8%
Aldose = 0.02%
Furanose = <0.2%

Question 7

Alcohols: High or low pKa?

Answer 7

High pKa

Question 8

2 ways to reduce the pKa of alcohols

Answer 8

1. Electron withdrawing groups through resonance

2. The inductive effect of electronegativity

Question 9

Why are alcohols polar?

Answer 9

Oxygen atom is highly electronegative

Question 10

2 ways of alcohol synthesis

Answer 10

1. Nucleophilic substitution of an alkyl halide

2. Acid catalysed hydration of alkenes

Question 11

Draw serine protease

Question 12

Draw oxidation of an alcohol to an aldehyde

Question 13

Draw dehydration of an alcohol to an alkene

Question 14

Draw phosphorylation of glucose

Question 15

How is glucose formed?

Answer 15

Photosynthesis

Question 16

Opposite of photosynthesis

Answer 16

Respiration

Question 17

3 classes of sugars

Answer 17

monosaccharides, disaccharides, polysaccharides

Question 18

Components of plant starch

Answer 18

amylose and amylopectin

Question 19

What is cellulose?

Answer 19

plant-based polymer of gluscose

Question 20

How is glucose stored?

Answer 20

As glycogen

Question 21

Which conformations can rings form?

Answer 21

chairs, boats, half-chair and twist-boat

Question 22

Rank the following alcohols in order of solubility, with 1 being the most soluble and 4 being the least soluble.
Hexanol
Octanol
Ethanol
Methanol

Answer 22

Methanol - Ethanol - Hexano - Octanol