4.1.2
Alkanes
OCR 4.1.2 covers alkanes as saturated hydrocarbons with σ-bonds and a tetrahedral shape, the boiling-point trends explained by London forces, why alkanes are so unreactive, their complete and incomplete combustion as fuels, and radical substitution with chlorine and bromine under ultraviolet light.
Revision Notes
Work through each part of OCR 4.1.2 in a structured sequence.
Oil
Alkanes from Crude Oil
Fractional distillation, cracking and reforming: where alkanes come from and how fractions are processed.
Start revisingas Fuel
Alkanes as Fuel
Complete and incomplete combustion, oxides of sulfur and nitrogen, and catalytic converters.
Start revisingAlternative Fuel
Biofuels, hydrogen and carbon neutrality compared with fossil fuels (extension for this board).
Start revisingSubstitution
Reactions of Alkanes
Free-radical substitution with halogens under UV light: initiation, propagation, termination and further substitution.
Start revisingShape
Bonding, Shape and Properties of Alkanes
σ-bonds and free rotation, the tetrahedral shape, boiling points and London forces, and why alkanes are unreactive (4.1.2(a)-(d)).
Start revising4.1.2 Alkanes – OCR A Level Chemistry A
The following OCR specification points outline the knowledge and skills students are expected to demonstrate for Alkanes.
4.1.2 Alkanes
Alkanes as saturated hydrocarbons containing single C-C and C-H bonds as σ-bonds (overlap of orbitals directly between the bonding atoms); free rotation of the σ-bond.
Explanation of the tetrahedral shape and bond angle around each carbon atom in alkanes in terms of electron pair repulsion.
Explanation of the variations in boiling points of alkanes with different carbon-chain length and branching, in terms of induced dipole-dipole interactions (London forces).
The low reactivity of alkanes with many reagents in terms of the high bond enthalpy and very low polarity of the σ-bonds present.
Complete combustion of alkanes, as used in fuels, and the incomplete combustion of alkane fuels in a limited supply of oxygen with the resulting potential dangers from CO.
The reaction of alkanes with chlorine and bromine by radical substitution using ultraviolet radiation, including a mechanism involving homolytic fission and radical reactions in terms of initiation, propagation and termination.
The limitations of radical substitution in synthesis by the formation of a mixture of organic products, in terms of further substitution and reactions at different positions in a carbon chain.
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