Friday 1 April 2016

3.7 draw displayed formulae for alkenes with up to four carbon atoms in a molecule, and name the straight-chain isomers (knowledge of cis- and trans-isomers is not required

This one gets a bit more confusing than alkanes. Alkenes have one carbon-carbon double bond in their carbon chain (this means they are saturated).

alkeneformulachemical structureball-and-stick model
etheneC2H4ethene has 2 carbon atoms and 4 hydrogen atomsthe carbon atoms are joined by a double bond
propeneC3H6propene has 3 carbon atoms and 6 hydrogen atomstwo of the carbon atoms are joined by a double bond
buteneC4H8four C's and eight H'sfour carbon atoms and eight hydrogen atoms

There are two possibilities for butene as the carbon-carbon double bond can go in two places.

NOTE: Ethene is the first alkene as 'methene' can not exist. This is because alkenes have carbon-carbon double bonds and 'methene' would only have 1 carbon, with no double bond.
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