Organic chemistry

Organic chemistry in the first year of the A level course lays a foundation of understanding which is crucial for the remainder of the course. The nomenclature learned at GCSE for hydrocarbons is extended and refined. It is important that students' understanding of nomenclature is clear and thorough, since the nomenclature of all organic compounds is an extension of that learned for alkanes and alkenes at this early stage. Isomerism is developed to include different types of structural isomers including chain (skeletal), functional group and position isomers. Students are also introduced to one type of stereoisomerism, geometric isomerism. The other type of streoisomerism is optical isomerism which is developed in year two.

The third fundamental concept that students are introduced to is that of reaction mechanisms, and this is not a concept that students will have encountered earlier at GCSE. So these three pillars, nomenclature, isomerism and reaction mechanisms are the basic structures upon which an understanding of organic chemistry is built. Their importance cannot be overstated and students who master these principles early will find organic chemistry much easier to cope with. Without them, the subject collapses to a collection of facts and 'recipes'.

Organic molecules are three dimensional, and bear little resemblance to the displayed formulae that are written down. and students need to be encouraged from the outset to think of molecules in three dimensions as this will make subsequent understanding of aspects of mechanism much easier, and it becomes essential when optical isomerism is introduced in year two of the course.

In terms of functional group chemistry it is helpful to think in terms of an analogy with group chemistry in the periodic table. The group determines the chemistry (how the element reacts) and the period affects the kinetics. In oganic chemistry the functional group is largely responsible for the chemistry and the rest of the molecular framework modifies physical properties such as solubility and the kinetics of the reactions.

These fundamentals are then continuously applied to the development of an understanding of the chemistry of just four functional groups: alkanes, alkenes, alcohols and halogenoalkanes.

Four mechanisms must be studied in the first year; radical substitution, nucleophilic substitution, electrophilic addition, and elimination. The first is not generally useful as it applies only to alkanes (radical mechanisms per se is a much bigger topic, but is rather limited at A level).

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