14.2 – Introduction to organic compounds

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1. Identify and draw the structures of methane, ethane, ethene and ethanol.

(Don’t panic. You’ll understand these figures in more detail at the end of this topic!)

Methane – CH₄ :

 

Ethane – C₂H₆ :
Ethene – C₂H₄ :

Ethanol – C₂H₅OH :

2. Describe the concept of homologous series of alkanes and alkenes as families of compounds with similar properties.

Hydrocarbons are known as organic compounds, and they’re classified into homologous groups. Examples of homologous groups are alkanes and alkenes. Compounds in each homologous series have

• the same chemical reactions
• the same functional group (Eg. –OH, ‐COOH)
• the same general formula examples-  Alkanes: C_nH_(2n+2) , Alkenes: C_nH_2n)
• similar, albeit slightly different,  physical properties

3. State the type of compound present, given a chemical name ending in -ane, -ene and -ol, or a molecular structure.

Alkanes are compounds that only contain hydrogen and carbon and possess no double bonds. They are saturated (by having only carbon single bonds, they have bonded with the maximum number of atoms). Their general formula is C_nH_(2n+2) . Examples are methane(CH₄), ethane (C₂H6), propane (C₃H₈) and butane (C₄H₁₀).
(Notice how the carbon atoms start at one and increase by one with each alkane. Their formulae also follow the general alkane formula).

Alkenes are compounds that only contain hydrogen and carbon but do possess one or more double bonds. They are unsaturated (by possessing one or more carbon double bonds, they have not bonded with the maximum number of atoms). Their general formula is C_nH_2n . Examples are ethene (C₂H₄), propene (C₃H₆) and butene (C₄H₈).
(Notice how the carbon atoms start from 2 and increase by one with each alkene. They too follow the general alkene formula).

Alcohols are compounds that contain hydrogen and carbon but also possess one hydroxyl group (-OH). Their general formula is C_nH_(2n+1)OH. Examples are methanol (CH₃OH), ethanol (C₂H₅OH) and propanol (C₃H₇OH).
(The carbon atoms start from 1 and increase by one with each alcohol. They too follow the general alcohol formula).

 

4. Name, identify and draw the structures of the unbranched alkanes and alkenes (not cis-trans), containing up to four carbon atoms per molecule.

(Tip:
‘meth’ – 1 carbon atom
‘eth’ – 2 carbon atoms
‘prop’ – 3 carbon atoms
‘but’ – 4 carbon atoms)

 

Notes submitted by Lintha

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