Straight Chain Isomers
other than diff. placements of alkyl groups, different placements of the functional group C=C also gives rise to isomerism
In butene → the C=C bond can be placed at the side or in the centre → giving rise to 2 straight chain isomers of butene → but-1-ene and but-2-ene.
Branched Chain Isomers
- Branched chain isomers can be drawn by shifting placement of alkyl groups in straight chain butene.
Steps to deduce the full structural formula of the branched chain isomer of butene
| Step | Explanation | Diagram |
|---|---|---|
| 1 | Draw main carbon chain. It should only have 3 carbons There is only 1 way to place the double bond here as placing double bond between C2 and C3 will lead to same structure. |  |
| 2 | Determine position of side chain. to make a branched isomer → side chain can only be attached to C2 attaching side chain to carbons C1 and C3 → which are located at ends of main carbon chain → will give you structure of straight chain alkene. |  |
| 3 | add in the hydrogen atoms such that all carbon atoms form 4 bonds. | thus, structural formulae of the branched chain isomer of butene is:  |
butene and but-2-ene
| Organic Compound | Butene | But-2ene |
|---|---|---|
| displayed formula / full structural formula |  |  |
Similarity:
- both have same molecular formula,
Differences:
| Organic Compound | Butene | But-2ene |
|---|---|---|
| structural formula | ||
| arrangement of atoms | - in this straight chain butene → position of functional group, carbon-carbon double bond → is between the 1st and 2nd carbon atoms in the carbon chain | - in this straight chain butene → position of functional group → carbon carbon double bond → is between 2nd and 3rd carbon atoms in carbon chain |
Sample
are these compounds isomers? explain
- Yes.
- both compounds have same molecular formula of
- but they have different structural formula. the position of the carbon-carbon double bond is between 1st and 2nd carbon atoms in butene but this functional group is between 2nd and 3rd carbon atoms in but-2ene.
