ChemistryCode 9701
Alkenes
What this topic asks you to be able to do
- recall how alkenes can be made, including the reagents and conditions: (a) elimination of HX from a halogenoalkane on heating with ethanolic NaOH (b) dehydration of an alcohol over a heated catalyst (e.g. Al2O3) or with a concentrated acid (e.g. concentrated H2SO4) (c) cracking a longer-chain alkane
- describe these reactions of alkenes: (a) electrophilic addition of (i) hydrogen, H2(g), with a Pt/Ni catalyst and heating, as a hydrogenation reaction (ii) steam, H2O(g), using an H3PO4 catalyst (iii) a hydrogen halide, HX(g), at room temperature (iv) a halogen, X2 (b) oxidation with cold dilute acidified KMnO4, forming the diol (c) oxidation with hot concentrated acidified KMnO4, which splits the carbon–carbon double bond, after which the products formed are identified to locate the alkene linkages in larger molecules (d) addition polymerisation, with ethene and propene as examples
- describe how aqueous bromine is used to test whether a C=C bond is present
- describe the electrophilic addition mechanism in alkenes, taking the reactions of bromine with ethene and of hydrogen bromide with propene as examples
- describe and explain how alkyl groups, through their inductive effects, alter the stability of the tertiary, secondary and primary cations formed in electrophilic addition, and use this to explain Markovnikov addition