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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Links and Resources
This resource provides a very rich source of worksheets covering almost all of the topics relevant to first year organic chemistry.The material could be useful to reinforce learning either in class or as homework exercises.
The only reactions of alkanes are combustion reactions and radical substitution, making them rather bland and uninteresting molecules from a chemical perspective.
This resource explains how to make magnesium silicide, which reacts with water under acidic conditions to produce silane (SiH4), which is the silicon analogue of methane. Silane combusts spontaneously in air whereas methane does not. The experiment stimulates a discussion of why this should be so.
This is interesting because there is not much practical chemistry that can be done in the section on alkanes and it also gets students to think about why this should be so (alkanes have no significant bond dipoles due to the similar electronegativities of carbon and hydrogen; 2.5 and 2.1 respectively on the Pauling scale).
This resource asks students to look at two reaction mechanisms, electrophilic addition to an alkene and radical substitution of an alkane. Worksheets are provided with alternative reaction schemes for the mechanisms and students are expected to select the correct mechanism from several plausible possibilities and explain why.
This has been used as a diagnostic to probe students' understanding of mechanism and a short discussion of findings is included.
In this activity students polymerise phenylethene to produce polyphenylethene (styrene). The resource states that the experiment is only suitable for very able students but does not say why. Presumably this is to ensure safe handling of the reactants. Exposure could be minimised by preparing the boiling tubes in advance and stoppering and providing students with pre-weighed vials containing initiator. Students would then only need to open the boiling tube long enough to add the initiator from the vial, thus minimising exposure.
This interesting resource explores the story around the fortuitous discovery of Teflon (PTFE), and reinforces the occasional importance of serendipity in scientific progress.
Students will probably have met PTFE as a polymer at GCSE, but will probably be unaware of the story of it discovery.
This simple activity introduces alcohols by looking at some of the chemical and physical properties of ethanol including its flammability, miscibility with water, acid-base properties and its facile oxidation to an aldehyde.
The resource includes student work sheets with instructions for the activity and brief teachers' notes.
In this simple microscale experiment cyclohexanol is oxidised by acidified potassium dichromate. The students worksheet gives full instructions for the task.
This is a problem solving exercise, giving students an opportunity to practice ideas related to alcohols in an investigative project.
Samples of artificial vodka are distilled to separate out the alcohols which they contain and the two alcohols identified by test tube reactions. The iodoform reaction is employed, which students will no longer be familiar with.
One solution is to add the test to the information given to the students.
Student task sheets and teachers' notes are included.
This is a relatively recent factsheet (2010) on bioethanol, its production, uses and importance. It could be used as a primer in a lesson discussing alternative fuels of chemical feedstocks.
This comprehensive resource provides much detailed background material on halogenoalkanes and alcohols. The resource would be useful for teachers when planning lessons for this module, but also many of the exercises, with a few dated exceptions, are still useful and pertinent to current syllabuses and can be scanned or retyped and edited to provide class or homework material. An invaluable resource for planning, and for setting example problems to support teaching and learning.
Experiment one on page seven outlines the hydrolysis of a halogenoalkane and the identification of the halide liberated. In experiment tow on page seventeen students synthesise a halogenoalkane from the corresponding alcohol.