Hydrocarbons are a subgroup of organic compounds composed entirely of only carbon and hydrogen atoms. They can be simple or complex. They are generally classified into four subcategories namely
An example of a hydrocarbon is shown in Figure 1. Salicylic acid, also shown in Figure 1, is an organic compound but is not a hydrocarbon because it contains an oxygen group.
Figure 1: Left: is a molecular structure that is a hydrocarbon, such as methane, propane, and 1-butene. Right: is the structure of salicylic acid, which is not a hydrocarbon.
Read on for some thoughts on why this can be a difficult topic for teachers and students, five suggestions for changing it, and thoughts on why virtual labs can make things easier.
Why hydrocarbon nomenclature and representation can be tricky to learn
There are three reasons in particular why hydrocarbon nomenclature can be difficult, even for the most diligent of students.
1. There is a need for a basic understanding of the classification of hydrocarbons
Hydrocarbons can contain single, double, or triple bonds, which determines the nomenclature of the compound.
Alkanes are straight-chain hydrocarbon molecules containing only single-bonded carbon atoms. When you name these molecules, the last syllable of the name is "ane".
Alkenes are straight-chain hydrocarbon molecules that contain at least one carbon with a double bond. When you name these molecules, the last syllable of the name is "ene".
Alkynes are straight-chain hydrocarbon molecules that contain at least one carbon triple bond. When you name these molecules, the last syllable of the name is "yne".
Aromatic Hydrocarbons: Hydrocarbon with one or more rings. It may contain a single, double or triple bond.
Note: Alkanes are the least reactive hydrocarbons due to their stability. They contain only strong single sigma bonds. Single bonds require a lot of energy to break and are therefore the least reactive.
Figure 2: Role of the prefixes in names of hydrocarbons.
A hydrocarbon is saturated if it contains no double or triple bonds. When any of these are present in the compound, it becomes unsaturated. The molecular formulas of non-cyclic alkanes follow this rule for the amount of carbon and hydrogen: CnH2n+2. Noncyclic alkenes follow this rule: CnH2n. Noncyclic alkynes follow this rule: CnH2n-2.
2. It involves functional groups
The functional group is the part of the molecule that is responsible for its reactivity. Different functional groups cause different types of reactions in organic chemistry. The functional group can be a specific arrangement of carbon and hydrogen, e.g. double bonds, or may also contain other elements. Oxygen and nitrogen are the most common elements in organic compounds, apart from carbon and hydrogen. Other examples of elements are phosphorus and halogens.
3. It includes suffixes and prefixes in its nomenclature
Simple hydrocarbons are named using a few simple rules. The first part of the name - the prefix - is determined by the number of carbon atoms in the longest carbon chain. A prefix is added to the last syllable to indicate the number of carbon atoms in the hydrocarbon chain. The table below shows the prefixes for hydrocarbons with 1-10 carbon atoms in the longest carbon chain. Note that the second column shows only the prefix and the full name includes the suffix, which for a hydrocarbon depends on whether there are double or triple bonds in the compound.
The second part of the name - the suffix - is determined by whether double or triple bonds are present. A visual representation of these principles can be seen below
Figure 5: Overview of the nomenclature principles of simple hydrocarbons.
Only the carbon and hydrogen side groups in organic compounds have the same prefix as the hydrocarbon and the suffix '-yl' is used.
5 ways to make hydrocarbon nomenclature and representation a more approachable topic
With these points in mind, here are five things you can consider introducing into your chemistry class lessons to make them more engaging, approachable, and enjoyable to teach for you and to learn for your students.
1. Show the people behind the science
Antoine-Laurent Lavoisier was born into a privileged family on August 26, 1743, in the French capital, Paris.
His father was Jean-Antoine Lavoisier, a lawyer in the Paris Parliament. His mother was Emily Puntis, whose family fortune came from a butcher shop. She died when Antoine was five years old, leaving him a large sum of money.
Lavoisier studied law to please his family but was especially interested in science. He proposed the law of mass conservation. Lavoisier spent a lot of time isolating elements and breaking down chemical compounds. He discovered a system of naming chemical compounds consisting of several elements. Most of the systems are still in use today. He also named the element hydrogen.
2. Apply lessons to the real world
Hydrocarbons are very useful in our everyday lives. For instance, we need some energy to carry out our daily activities. This energy could be in the form of fuels for powering mechanical and electrical activities that enable us to drive to and from work, power machinery, etc
Hydrocarbons are mostly used for fuel. Gasoline, diesel fuel, natural gas, fuel oil, jet fuel, coal, kerosene, and propane are some commonly used hydrocarbon fuels. Hydrocarbons are also used to make things, including plastics, glue, and synthetic fabrics like polyester.
3. Explain the numbering rules in hydrocarbon nomenclature and the concept of isomerism.
When side groups are present on the longest chain of carbon atoms, they are numbered according to the carbon to which they are attached. The carbon number for this group of organic compounds is thus assigned:
You always count from one end of the longest carbon chain with the most important functional group.
If a double or triple bond is present, the counting should start from the end closest to this bond.
If only single bonds are present, the side groups should get the lowest number possible.
A number is included for each multiple bonds in the chain. The numbers are separated by commas. If more than one location is possible for a double or triple bond, a number is added to indicate its placement on the carbon chain, always counting from one end of the chain and giving the carbon the lowest number possible.
A hyphen links the number of location(s) to the hydrocarbon name.
For ring hydrocarbons (excluding aromatics such as benzene), attach "cyclo" as the first syllable.
If a side group can only be positioned in one place in the compound, the number can be omitted.
Structural isomers are compounds that have the same molecular formula but different atomic arrangements. There are several subgroups of structural isomerism. In chain isomers, the carbon skeleton of the compound is rearranged but still contains the same number of carbon and hydrogen atoms.
Figure 6: Examples of pairs of chain isomers. The first two compounds both have the formula C4H10, and the last two compounds both have the formula C6H14.
Another type of structural isomer is the positional isomer, which is based on the position of the functional group in the molecule. This position changes the name of the molecule slightly to indicate where the functional group is located and can have a major impact on reactions involving the molecule. 1-Butene and 2-butene are position isomers because the double bonds are positioned differently in identical compounds.
Branched-chain hydrocarbons are sometimes named for the prefix they would receive if all the carbons were in one chain. for example, methylpropane, which has four carbon atoms, is also often called isobutane, where iso means the structural isomer of butane, which can only be methylpropane.
4. Use skeletal formulas
A skeletal formula is a simple representation of an organic compound. Instead of listing all the carbon and hydrogen atoms, they are indicated by angles, also called "vertices," on the structure. For example, see Figure 7. Only carbon and hydrogen can be removed in this way.
Figure 7: The organic molecule benzene with all atoms drawn out (Structure A), and the simplified skeletal structure (Structure B), which is commonly used. The skeletal structure of salicylic acid with molecular formula C7H6O3(Structure C)
Skeletal structures are a great way to show important aspects such as the functional groups of an organic compound.
5. Encourage the use of virtual lab simulations
A unique way to teach about hydrocarbon nomenclature and representation is through a virtual laboratory simulation. At Labster, we’re dedicated to delivering fully interactive advanced laboratory simulations that utilize gamification elements like storytelling and scoring systems, inside an immersive and engaging 3D universe.
Check out the Labster hydrocarbon nomenclature and representation simulation that allows students to learn about hydrocarbon nomenclature through active, inquiry-based learning. In the simulation, students will learn how to name hydrocarbons - the core part of organic compounds. You will also be challenged with various ways of representing chemical structures in 2D, and learn to decide when to use which one.
Learn more about the hydrocarbon nomenclature and representation simulation here or get in touch to find out how you can start using virtual labs with your students.