Higher alkane

Key takeaways

Higher alkane belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Higher alkane to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Higher alkane from memory before moving on to harder problems.

Reference excerpt

Higher alkanes are alkanes with a high number of carbon atoms. It is common jargon. One definition says higher alkanes are alkanes having nine or more carbon atoms. Thus, according to this definition, nonane is the lightest higher alkane. As pure substances, higher alkanes are rarely significant, but they are major components of useful lubricants and fuels.

Synthesis The preparation of specific long-chain hydrocarbons typically involves manipulations of long chain precursors or the coupling of two medium-chain components. For the first case, fatty acids can be a source of higher alkanes via decarboxylation reaction. Such processes have been investigated as a route to biodiesel. Fatty acid esters and fatty acid nitriles react with long chain Grignard reagents to give, after suitable workup, long-chain ketones. The Wolff-Kishner Reaction provides a way to remove the ketone functionality, giving long-chain hydrocarbons. Even-numbered, long-chain hydrocarbons can also be synthesized through electrolysis and the Wurtz reactions of alkyl bromides.

Occurrence Higher alkanes can also be isolated and purified from natural or synthetic mixtures. Coal tar is a traditional source of mixtures of long-chain hydrocarbons. Careful fractionation, first using urea clathrates to remove branched hydrocarbons, and then distillation, produces pure n-hydrocarbons from petroleum. Regarding synthetic sources, the Fischer-Tropsch process (or FT process) produces a mixture of hydrocarbons by the hydrogenation of carbon monoxide. The products obtained are liquid hydrocarbons and waxy solids, mostly n-paraffins. The liquid fraction ranges from C6 to C20, while the solid fraction consists of hydrocarbons above C21.

Bioactivity Some branched higher alkanes are insect pheromones. 7-methyltricosane and 9-methyltricosane are active for ladybird beetles (Adalia bipunctata). The emerald ash borer (Agrilus planipennis Fairmaire) responds to 9-methylpentacosane. Female Asian long-horned beetles Anoplophora glabripennis, which are very damaging, secrete 2-methyldocosane.

Reactions Higher alkanes in general are relatively inert, just like low molecular weight alkanes they can react with oxygen and start a combustion reaction. They can undergo cracking in the presence of alumina or silica catalysts, forming lower alkanes and alkenes.

Uses Alkanes from nonane to hexadecane (those alkanes with nine to sixteen carbon atoms) are liquids of higher viscosity, which are less suitable for use in gasoline. They form instead the major part of diesel, kerosene, and aviation fuel. Diesel fuels are characterised by their cetane number, cetane being an older name for hexadecane. However the higher melting points of these alkanes can cause problems at low temperatures and in polar regions, where the fuel becomes too thick to flow correctly. Mixtures of the normal alkanes are used as boiling point standards for simulated distillation by gas chromatography. Alkanes from hexadecane upwards form the most important components of fuel oil and lubricating oil. In latter function they work at the same time as anti-corrosive agents, as their hydrophobic nature means that water cannot reach the metal surface. Many solid alkanes find use as paraffin wax, used for lubrication, electrical insulation, and candles. Paraffin wax should not be confused with beeswax, which consists primarily of esters. Alkanes with a chain length of approximately 30 or more carbon atoms are found in bitumen (asphalt), used (for example) in road surfacing. However, the higher alkanes have little value and are usually split into lower alkanes by cracking.

Names Some alkanes have non-IUPAC trivial names:

cetane, for hexadecane cerane, for hexacosane

Properties

Nonane is the lightest alkane to have a flash point above 25 °C, and is classified as flammable under the US National Library of Medicine. The properties listed here refer to the straight-chain alkanes (or: n-alkanes).

Nonane to hexadecane This group of n-alkanes is generally liquid under standard conditions.

Heptadecane to tetracosane From this group on, the n-alkanes are generally solid at standard conditions.

a

Pentacosane to triacontane

Hentriacontane to hexatriacontane

Heptatriacontane to dotetracontane

Tritetracontane to octatetracontane

Nonatetracontane to tetrapentacontane

Pentapentacontane to hexacontane

See also Alkene Alkyne Cycloalkane Hydrocarbon Paraffin wax, composed mostly of higher linear alkanes Polyethylene, a linear alkane of polymeric length

References

External links

International Chemical Safety Card 1245 (nonane) NIOSH Pocket Guide to Chemical Hazards (nonane) International Chemical Safety Card 0428 (decane)

Worked examples

Example 1 — a first encounter with Higher alkane

Start with the simplest possible case. Write down what Higher alkane claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Higher alkane before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Higher alkane ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Higher alkane

In research: Higher alkane appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Higher alkane in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Higher alkane is common in secondary-school and first-year university syllabi. It links to neighbouring topics Alkanes, so understanding it makes those chapters shorter.
In everyday life: Look for Higher alkane outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Higher alkane in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Higher alkane means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Higher alkane out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Higher alkane in simple terms?

Higher alkanes are alkanes with a high number of carbon atoms. It is common jargon.

Why does Higher alkane matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Higher alkane?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Higher alkane.