Unsaturated hydrocarbons
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Introduction
Isomerism
Alkenes: carbon-carbon double bond (σ + π-bond).
Alkynes: carbon-carbon triple bond (σ + 2 π-bonds).
Base of name will be the chain with the most unsaturation.
The double bond has priority over the triple bond and will form the base of the name.
The root chain is numbered from the end nearest a double bond carbon atom.
Examples of unsaturated hydrocarbons
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Rules for determining priorityAlkenes where the double bond has more than one substituent can exist in conformers with different geometries. This is called isomerism.
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© University of Borås
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Which group has the highest priority? The substituents look like this:
- = C - CH2 - CH3
- = C - CH3
First atom attached to the double bonded C is C for both groups.
Second atom in the sequence is C in the first case and H in the second case
C has higher priority than H and the ethyl group is consequently the dominating group.
Rules for determining priority:
- Look at atoms directly bonded to the double-bonded carbons – rank according to atomic number (the higher number the higher priority).
- If the directly bonded atoms are the same look at the second, third and fourth atoms away from the double bonded carbon until first difference is found.
- Multiple-bonded atoms are equivalent to the same number of single bonded atoms.
How shall we draw 3-hexyl-6,6-dimethyl-1,3-heptadien?
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Project
Contact
This resource was developed as part of an Erasmus+ project, funded with support from the European Commission under grant agreement 2016-1-SE01-KA203-22064.
The project was a collaboration between:
- The University of Borås, Sweden
- The University of the Highlands and Islands, Scotland
- The University of Alcalá, Spain
- Digital Connections, Scotland
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