3.2.11—Reduction of unsaturated compounds
- Syllabus
- First assessment 2025
- Objective
- 3.2.11
- Level
- SL
Hydrogenation of Alkenes and Alkynes
Hydrogenation adds H2 across π bonds. Continue addition until the required saturated product is formed; nickel, palladium or platinum catalysts with heat or pressure are typical conditions.
Count π bonds to determine hydrogen demand: one mole of H₂ saturates one C=C, while full conversion of one C≡C to C–C needs two moles of H₂. Keep the carbon skeleton unchanged when drawing the product.
Deducing Hydrogenation Products
Assessment in practice
Representative question
Question 1
[Maximum number: 2]
State the reagent and conditions needed and draw the structural formula of the product.
Official product structure shown in the figure.
Reagent:
H2 with Ni, Pd or Pt catalyst
Product:
CH3CH2CH2CH2CH2CH3
Accept the condensed formula CH3(CH2)4CH3.
Electron Transfer Reactions Summary
Retrieve the route: assign oxidation states, balance half-equations, predict displacement, label cells, trace electrons and ions, follow organic redox pathways, calculate potentials and choose electrolysis products.
Check electron loss/gain, anode/cathode versus polarity, spontaneous sign, salt-bridge direction, ions present, organic functional-group direction and object-cathode placement.