Nimo

Study smarter with Nimo

Personalised revision that adapts to you. Ace your revision with unlimited practice questions that are designed to help you learn faster. We're slowly rolling out to more and more students.

Try Nimo

Alkene addition reactions and conditions

Organic chemistry • Reactions of alkenes and alcohols

Key concepts

What you'll likely be quizzed about

  • Hydrogenation converts an alkene to an alkane by adding H2 across the C=C double bond.
  • The π bond breaks, forming two new C–H σ bonds.
  • This process requires molecular hydrogen and a metal catalyst that adsorbs both hydrogen and alkene, promoting the addition of hydrogen atoms to the carbons.
  • Nickel, palladium, or platinum act as common catalysts.
  • Laboratory hydrogenation typically uses platinum or palladium at mild temperatures, while industrial hydrogenation usually involves a nickel catalyst at elevated temperatures to improve reaction rates.
  • Increasing hydrogen pressure enhances the reaction rate because higher concentration promotes more effective collisions.
  • The reaction proceeds via surface-catalysed addition, contrasting with free radical methods, making catalysts and H2 limiting factors in the process.

Flashcards

Test your knowledge with interactive flashcards

What product forms when an alkene reacts with chlorine (Cl2)?

Click to reveal answer

A vicinal dichloride is produced, with chlorine atoms added to each of the former double-bonded carbons.

Key notes

Important points to keep in mind

Electrophilic addition occurs because the π bond is electron-rich and easily attacked by electrophiles.

Hydrogenation requires H2 and a metal catalyst (Ni, Pt, or Pd); pressure and temperature influence the rate.

Hydration follows Markovnikov orientation; acid catalysts form carbocations that determine product placement.

Steam hydration utilizes phosphoric acid catalysts at high temperature and pressure in industrial settings.

Halogenation employs X2 (Br2, Cl2) and proceeds through a cyclic halonium ion, resulting in anti addition.

Bromine water decolourisation serves as a quick test for unsaturation (alkenes).

Carbocation intermediates allow rearrangements; monitor conditions to minimise undesired shifts.

Catalyst choice affects temperature requirements and reaction selectivity.

More substituted alkenes generally react faster in electrophilic addition due to greater carbocation stability.

Solvent and safety considerations influence reagent choices; avoid toxic solvents in practical work.

Regiochemistry depends on intermediate stability; consider electronic and steric factors.

Industrial conditions differ from laboratory methods to optimise yield.

Built with v0