Organic Synthesis and Analyisis

Question 1

How do you synthesise stuff?

Answer 1

Question 2

How do you synthesise aromatic stuff?

Answer 2

Question 3

What is the chemical test for an alkene? (–C=C–)

Answer 3

• Shake with bromine water.
• The solution turns colourless if the substance is unsaturated, from red-brown to colourless.

Question 4

What is the chemial test for a haloalkane?

Answer 4

1. Add NaOH(aq) and warm (gets the halogen off the haloalkane and into the solution as a halide ion)
2. Add nitric acid, HNO3 (rids of any ions; carbonates, sulfates etc. that would interfere with taste and give a false reading)
3. Add silver nitrate solution, AgNO₃(aq).

Colour of precipitate of silver halide tells you which halide it is:
F^- No precipitate
Cl^- White (dissolves in dil. ammonia solution)
Br^- Cream (dissolves in conc. ammonia solution)
I^- Yellow (insoluble in conc. ammonia solution)

Add ammonia solution to test the solubility if unsure of the colour.

Question 5

What is the test for an alcohol? (R–OH)

Answer 5

• Warm with K₂Cr₂O₇/H⁺
  (acidified potassium dichromate)
• Orange colour turns green with primary or secondary alcohols (also with aldehydes)

Question 6

What is the test for Aldehydes? (R–CHO)

Answer 6

• Warm with Tollens’ reagent
• Silver mirror forms with aldehyde, no change with ketone

Question 7

What is the test for carboxylic acids? (R–COOH)

Answer 7

• Add NaHCO₃(aq)
  (sodium bicarbonate)
• CO₂ is given off

Question 8

What is the test for acyl chlorides? (R–COCl)

Answer 8

• Add AgNO_3(aq)
  (silver nitrate solution)
• White precipitate of AgCl forms (like haloalkane reaction); vigorous.

Question 9

How do you calculate percentage yield?

Answer 9

% yield = actual yield
theoretical yield x 100

Question 10

How do you calculate atom economy?

Answer 10

% atom economy = mass of desired product
total mass of reactants x 100

Mass can be in grams or total Mr.