Functional group chemistry

Nature of science:

Use of data—much of the progress that has been made to date in the developments and applications of scientific research can be mapped back to key organic chemical reactions involving functional group interconversions. (3.1)

• Alkanes have low reactivity and undergo free-radical substitution reactions.

Alkenes:

• Alkenes are more reactive than alkanes and undergo addition reactions. Bromine water can be used to distinguish between alkenes and alkanes.

Alcohols:

• Alcohols undergo nucleophilic substitution reactions with acids (also called esterification or condensation) and some undergo oxidation reactions.

Halogenoalkanes:

• Halogenoalkanes are more reactive than alkanes. They can undergo (nucleophilic) substitution reactions. A nucleophile is an electron-rich species containing a lone pair that it donates to an electron-deficient carbon.

Polymers:

• Addition polymers consist of a wide range of monomers and form the basis of the plastics industry.

Benzene:

• Benzene does not readily undergo addition reactions but does undergo electrophilic substitution reactions.

• Methane is a greenhouse gas, and its release from ruminants in countries such as Brazil, Uruguay, Argentina and New Zealand contributes significantly to total greenhouse gas emissions. Landfills are also a source of methane, and technologies are developing in some countries to capture the gas as a source of energy for electricity and heat generation.
• Alcohol misuse is a growing problem in many countries and can have an impact on their economies and social structures.

Utilization:

• Alkane usage as fuels.
• The role of ethene in fruit ripening.
• Alcohols, usage as fuel additives.
• Alcohols, role in the breathalyser.
• Esters, varied uses—perfumes, food flavourings, solvents, nitroglycerin, biofuels and painkillers.

Syllabus and cross-curricular links:
Topic 9.1—redox processes
Option A.5—polymers
Option B.3—lipids

• Writing equations for the complete and incomplete combustion of hydrocarbons.
• Explanation of the reaction of methane and ethane with halogens in terms of a free-radical substitution mechanism involving photochemical homolytic fission.

Alkenes:

• Writing equations for the reactions of alkenes with hydrogen and halogens and of symmetrical alkenes with hydrogen halides and water.
• Outline of the addition polymerization of alkenes.
• Relationship between the structure of the monomer to the polymer and repeating unit

. Alcohols:

• Writing equations for the complete combustion of alcohols.
• Writing equations for the oxidation reactions of primary and secondary alcohols (using acidified potassium dichromate(VI) or potassium manganate(VII) as oxidizing agents). Explanation of distillation and reflux in the isolation of the aldehyde and carboxylic acid products.
• Writing the equation for the condensation reaction of an alcohol with a carboxylic acid, in the presence of a catalyst (eg concentrated sulfuric acid) to form an ester.

Halogenoalkanes:

• Writing the equation for the substitution reactions of halogenoalkanes with aqueous sodium hydroxide.

• Aim 6: Experiments could include distinguishing between alkanes and alkenes, preparing soap and the use of gravity filtration, filtration under vacuum (using a Buchner flask), purification including recrystallization, reflux and distillation, melting point determination and extraction.
• Aim 8: Discuss the significance of the hydrogenation of alkenes in the food production including trans-fats as by-products.

• Reference should be made to initiation, propagation and termination steps in free-radical substitution reactions. Free radicals should be represented by a single dot.
• The mechanisms of S_N1 and S_N2 and electrophilic substitution reactions are not required.