Organic Synthesis 4.2.3

Question 1

Define volatility

Answer 1

How easily a substance turns into a gas (this is directly related the boiling point).

Question 2

When talking about organic compound’s, how would you explain the differing boiling points?

Answer 2

IMF

Refer to number of electrons and surface contact between molecules.

Question 3

Comment on the relative water solubility of: butan-2-ol, 2,2-dichlorobutane and butene.

Answer 3

Butan-2-ol has an OH group so hydrogen bonding can occur with water, 2,2-dichlorobutane has permanent dipoles and butene has induced dipole dipole forces. So butan-2-ol is the most soluble.

Question 4

Explain with reasoning which of the following has the highest boiling point;
Pentane & 2,2-dimethylpropane

Answer 4

Both molecules have IDD forces. Pentane is a straight chain molecule so there is more surface contact therefore IDD forces are stronger and more energy is needed to overcome them, therefore it has a higher boiling point.

Question 5

What are the reagents and conditions for the following 2 reactions;

Alkane ➡️ Haloalkane

Alkane ➡️ CO2 +H2O

Answer 5

Alkane ➡️ Haloalkane
Reagents: Cl2
Conditions: UV Light

Alkane ➡️ CO2 + H2O
Reagents: Excess O2
Conditions: Heat

Question 6

State the reagents and conditions for the following reactions;
Alkene ➡️ Alkane
Alkene ➡️ Dihaloalkane
Alkene ➡️ Alcohol
Alkene ➡️ Chloroalkane
Alkene ➡️ CO2 + H2O

Answer 6

Reagents: H2 + Nickel Catalyst
Conditions: High Temperature

Reagents: Br2
Conditions: Room temperature/conditions

Reagents: H20 and H3PO4 catalyst
Conditions: High temperature

Reagents: HCl
Conditions: Room temperature/pressure

Reagents: Excess O2
Conditions: Heat

Question 7

State the reagents and conditions for the following;
Alcohol ➡️ CO2 + H2O
Alcohol ➡️ Aldehyde
Alcohol ➡️ Carboxylic Acid
Alcohol ➡️ Alkene
Alcohol ➡️ Haloalkane

Answer 7

Reagents: Excess O2
Conditions: Heat

Reagents: Cr2O7/H+
Conditions: distillation

Reagents: Cr2O7/H+
Conditions: Reflux

Reagents: Concentrated H2SO4
Conditions: 170•c

Reagents: NaBr, H2SO4

Question 8

State the reagents and conditions for the following;

Haloalkane ➡️ Alcohol

Answer 8

Reagents: NaOH (aq)
Conditions: Heat

Question 9

Suggest how ethanoic acid could be formed from chloroethane. You should identify the reagents, conditions and any intermediates formed.

Answer 9

Chloroethane ➡️ Alcohol
Reagents: NaOH (aq)
Conditions: Heat

Alcohol ➡️ Carboxylic Acid
Reagents: Acidified potassium dichromate
Conditions: reflux

Question 10

What chemical tests could you perform to distinguish between the following pairs;

Cyclohexane & Cyclohexene

1-Chlorobutane & 1-Bromobutane

Answer 10

1. Add bromine water and it will turn from orange to colourless if it’s Cyclohexene
2. Heat it with NaOH(aq) then add HNO3(aq) then add AgNO3(aq).
   Chloro ➡️ White ppt (soluble in dilute ammonia)
   Bromo ➡️ cream ppt (insoluble in dilute ammonia)

Question 11

Define structural isomer

Answer 11

Molecules with the same molecular formula but a different structural formula.

Question 12

What does a ‘curly arrow’ represent?

Answer 12

The movement of pairs of electrons.

Question 13

How could you distinguish between an aldehyde and a Carboxylic acid?

Answer 13

• Add Acidified Potassium Dichromate and the aldehyde will turn from orange to green
• Add Na2CO3, fizzing/bubbles
• pH acid 1, the aldehyde will be neutral
• The aldehyde will have a fruity smell whereas the acid will smell of vinegar (ethanoic acid)

Question 14

How can you purify the organic products from a reaction where water is usually a by-product?

Answer 14

Two layers will be seen in the reaction flask. You can identify the organic later by comparing densities or adding water and seeing which later will be bigger. Once you have identified the organic layer a separating funnel is used to separate the layers.

Question 15

Impure products often contain acid impurities, suggest a practical method to remove these impurities

Answer 15

Add Na2CO3(aq) - see fizzing (CO2 (g))
Add it until is stops fizzing

Question 16

How can you remove a small amount of water from the organic product?

Answer 16

By adding a drying agent, anhydrous inorganic salt that will take up water to become hydrated.
EXAMPLES
• Anhydrous Calcium Chloride
•Anhydrous Calcium Sulfate
Anhydrous magnesium Sulfate

Question 17

Once your sample has been dried it may still contain organic impurities that have similar boiling points. How would you make it purer?

Answer 17

You carry out a second distillation but this time you only collect the product with the boiling point of your compound. The narrower the boiling point range, the purer the product.

Question 18

Name the apparatus that could be used to separate the two liquid layers present at the end of the experiment

Answer 18

Separating Funnel

Question 19

Physical properties of molecules can be determined once you know the functional groups present in a molecule. What two properties can you then comment on?

Answer 19

Solubility in water

Volatility/boiling point