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14. Hydrocarbons

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  1. 14.1 Alkanes

    1. 14.1.1Preparation of alkanes

      • Recall preparation of alkanes: (a) addition of hydrogen to an alkene in a hydrogenation reaction, H2(g) and Pt/Ni catalyst and heat; (b) cracking of a longer chain alkane, heat with Al2O3

    2. 14.1.2Describe

      • Describe:: (a) the complete and incomplete combustion of alkanes; (b) the free-radical substitution of alkanes by Cl 2 or Br2 with ultraviolet light, as exemplified by the reactions of ethane

    3. 14.1.3Mechanism: free-radical substitution

      • Describe the mechanism of free-radical substitution using the initiation, propagation and termination steps

    4. 14.1.4Suggest how cracking can be used to obtain

      • Suggest how cracking can be used to obtain more useful alkanes and alkenes of lower M r from heavier crude oil fractions

    5. 14.1.5The general unreactivity of alkanes

      • Understand the general unreactivity of alkanes, including towards polar reagents in terms of the strength of the C–H bonds and their relative lack of polarity

    6. 14.1.6Combustion pollutants and catalysts

      • Recognise the environmental consequences of carbon monoxide, oxides of nitrogen and unburnt hydrocarbons arising from the combustion of alkanes in the internal combustion engine and of their catalytic removal

  2. 14.2 Alkenes

    1. 14.2.1Preparation of alkenes

      • Recall preparation of alkenes: (a) elimination of HX from a halogenoalkane by ethanolic NaOH and heat; (b) dehydration of an alcohol, by using a heated catalyst (e.g. Al2O3) or a conc. acid (e.g. conc. H2SO4); (c) cracking of a longer chain alkane

    2. 14.2.2Reactions of alkenes

      • Describe reactions of alkenes: - (a) the electrophilic addition of - (i) hydrogen in a hydrogenation reaction, H2(g) and Pt/Ni catalyst and heat - (ii) steam, H2O(g) and H3PO4 catalyst - (iii) a hydrogen halide, HX(g), at room temp. - (iv) a halogen, X2 - (b) the oxidation by cold dil. acidified KMnO4 to form the diol - (c) the oxidation by hot conc. acidified KMnO4 leading to the cleavage of the carbon–carbon double bond and the identities of the subsequent products to determine the position of alkene linkages in larger molecules - (d) addition polymerisation exemplified by the reactions of ethene and propene

    3. 14.2.3Of aq. bromine to show the presence of a C=C

      • Describe the use of aq. bromine to show the presence of a C=C bond

    4. 14.2.4Mechanism: electrophilic addition in alkenes,

      • Describe the mechanism of electrophilic addition in alkenes, using bromine/ethene and hydrogen bromide/propene as examples

    5. 14.2.5Inductive effects of alkyl groups

      • Describe/explain: the inductive effects of alkyl groups on the stability of primary, secondary and tertiary cations formed during electrophilic addition (this should be used to explain Markovnikov addition)