Topic 36: Organic Synthesis

Question 1

Definitions I:
(a) Functional group
(b) Synthetic route
(c) By-product

Answer 1

Definitions I:
(a) Group dictating chemical properties, e.g., -COOH.
(b) Multi-step sequence to make a target molecule.
(c) Secondary product from a reaction, e.g., HCl.

Question 2

Identify the functional groups in CH₃CH(OH)CH₂COOH using syllabus reactions. [2 Marks]

Answer 2

-OH (alcohol): Na → H₂; -COOH (acid): NaOH → salt (1 mark)
Both confirmed by syllabus tests (1 mark)

Question 3

Predict the reaction of CH₃COOCH₂CH₃ with NaOH(aq, heat) and name products. [2 Marks]

Answer 3

CH₃COOCH₂CH₃ + NaOH → CH₃COO⁻Na⁺ + CH₃CH₂OH (1 mark)
Sodium ethanoate, ethanol (1 mark)

Question 4

In a lab, devise a 2-step synthesis of CH₃CH₂NH₂ from CH₃CH₂Br. [2 Marks]

Answer 4

CH₃CH₂Br + NH₃ → CH₃CH₂NH₂ + HBr (ethanol, pressure, heat) (1 mark)
Step 1 only needed, simple SN (1 mark)

Question 5

Analyse this route: CH₃CH₂OH → CH₃CHO → CH₃COOH. Name reaction types and reagents. [3 Marks]

Answer 5

Step 1: Oxidation, K₂Cr₂O₇/H⁺, distil (1 mark)
Step 2: Oxidation, KMnO₄/H⁺, reflux (1 mark)
By-product: H₂O (1 mark)

Question 6

What functional groups are in CH₃CH₂CONH₂ and how do you test them? [2 Marks]

Answer 6

-CONH₂ (amide): NaOH → NH₃ (1 mark)
Test: hydrolysis, ammonia smell (1 mark)

Question 7

Predict the product of CH₃CH₂COCl with NH₃ and write the equation. [2 Marks]

Answer 7

CH₃CH₂COCl + NH₃ → CH₃CH₂CONH₂ + HCl (room temp) (1 mark)
Propanamide formed (1 mark)

Question 8

In a classroom, devise a 3-step synthesis of CH₃COOCH₃ from CH₃CH₂OH. [3 Marks]

Answer 8

CH₃CH₂OH → CH₃CHO (K₂Cr₂O₇/H⁺, distil) (1 mark)
CH₃CHO → CH₃COOH (KMnO₄/H⁺, reflux) (1 mark)
CH₃COOH + CH₃OH → CH₃COOCH₃ (H⁺, heat) (1 mark)

Question 9

What by-products form when CH₃COCl reacts with CH₃CH₂OH? [2 Marks]

Answer 9

CH₃COCl + CH₃CH₂OH → CH₃COOCH₂CH₃ + HCl (1 mark)
By-product: HCl (1 mark)

Question 9

Identify the functional group in CH₃CH₂CH(OH)CH₃ and predict its reaction with PCl₅. [2 Marks]

Answer 9

-OH (alcohol): CH₃CH₂CH(OH)CH₃ + PCl₅ → CH₃CH₂CHClCH₃ + POCl₃ + HCl (1 mark)
Substitution confirmed (1 mark)

Question 10

Predict the properties of CH₃CH₂COOH based on its functional group. [2 Marks]

Answer 10

-COOH: acidic, reacts with bases (1 mark)
Soluble in water, forms salts (1 mark)

Question 11

Analyse this route: C₆H₆ → C₆H₅NO₂ → C₆H₅NH₂. List reagents and by-products. [2 Marks]

Answer 11

C₆H₆ + HNO₃ → C₆H₅NO₂ (H₂SO₄, 25-60°C), H₂O (1 mark)
C₆H₅NO₂ + 6[H] → C₆H₅NH₂ (Sn/HCl, heat, NaOH), 2H₂O (1 mark)