Alkenes (Digital Notes)

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Alkenes are hydrocarbons that contain at least one carbon-carbon double bond (C=C). They are unsaturated compounds, meaning they can react with hydrogen, halogens, and other molecules to form new compounds. Alkenes are commonly found in various industrial processes and are key building blocks in organic chemistry, with ethene (ethylene) and propene being the simplest and most well-known examples.

Description

Course Contents

  • Alkenes (exemplified by ethene)
  • (i) electrophilic addition, including Markovnikov’s rule
  • (ii) reduction and oxidation reactions

 

Learning Outcomes

Candidates should be able to:

  • (a) explain the general reactivity of alkenes towards electrophilic reagents/electrophiles
  • (b) describe the chemistry of alkenes as exemplified, where relevant, by the following reactions of ethene:
  • (i) electrophilic addition of water/steam, hydrogen halides and halogens
  • (ii) reduction via catalytic hydrogenation (catalytic addition of hydrogen; see also 8(j))
  • (iii) oxidation by cold, alkaline solution of manganate(VII) ions to form the diol
  • (iv) oxidation by hot, acidified solution of manganate(VII) ions leading to the rupture of the carbon-to-carbon double bond in order to determine the position of alkene linkages in larger molecules
  • (c) describe the mechanism of electrophilic addition in alkenes, using bromine with ethene as an example
  • (d) apply Markovnikov’s rule to the addition of hydrogen halides to unsymmetrical alkenes, and explain the composition of products in terms of the stability of carbocation intermediates
  • (e) explain, in terms of delocalisation of π electrons, the difference between benzene and alkene:
  • (i) reactivity towards electrophiles
  • (ii) preference of benzene to undergo substitution rather than addition reaction