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WAChemistryQuick questions

Unit 4: Organic Chemistry and Chemical Synthesis

Quick questions on Hydrocarbons: alkanes, alkenes and alkynes: WACE Year 12 Chemistry

3short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What are alkanes?
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Alkanes contain only single carbon-carbon bonds and so are saturated (each carbon holds the maximum number of hydrogen atoms). Their general formula is CnH2n+2\text{C}_n\text{H}_{2n+2} (methane, ethane, propane and so on). Because the C-C and C-H single bonds are strong and non-polar, alkanes are relatively unreactive. Their main reactions are combustion and, with ultraviolet light, substitution with halogens.
What are alkenes?
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Alkenes contain at least one C=C double bond and are unsaturated, with general formula CnH2n\text{C}_n\text{H}_{2n} (ethene, propene and so on). The double bond is a region of high electron density and is the reactive site. Alkenes readily undergo addition reactions, in which a molecule adds across the double bond, converting it to a single bond.
What are alkynes?
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Alkynes contain a C≡C triple bond, general formula CnH2n2\text{C}_n\text{H}_{2n-2} (ethyne is the simplest). Like alkenes they are unsaturated and undergo addition, and they are even more unsaturated, so they can add two molecules across the triple bond.

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