Constitutional (structural) isomers have the same molecular formula but a different atom-to-atom bonding sequence.
Constitutionally isomeric alkenes may have different arrangement of carbons (carbon skeletons).
Constitutionally isomeric alkenes may have the same carbon skeleton with the double bond at a different position in the chain.
Note that there are only two different positions for the double bond for in a linear four-carbon chain because of the symmetry in the carbon chain.
Likewise the image below shows that there is only one type of adjacent carbon pair in a three-carbon chain with a methyl branch. Thus the only alkene with this carbon skeleton is methylpropene (also shown below).
Constitutionally isomeric alkenes may have different arrangement of carbons (carbon skeletons).
Example C4H8 constitutional isomers.
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Constitutionally isomeric alkenes may have the same carbon skeleton with the double bond at a different position in the chain.
Example C4H8 constitutional isomers.
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Note that there are only two different positions for the double bond for in a linear four-carbon chain because of the symmetry in the carbon chain.
The image shows the two different types of adjacent carbon pairs (blue/blue and red/blue).
Likewise the image below shows that there is only one type of adjacent carbon pair in a three-carbon chain with a methyl branch. Thus the only alkene with this carbon skeleton is methylpropene (also shown below).
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