How many stereoisomers of 2-chloro-5-fluoro-3-hexene are possible? and how can we count them when we have double bond ?

1 Answer
Apr 5, 2018

Consider the molecule you describe,

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Now, consider how many chirality centers it has (remember implied hydrogens).

It has 2, and by the #2^n# rule, we would have four possible stereoisomers without a double bond.

Now, consider the configuration of the double bond, the highest priority groups are on opposite sides. If we rotated the double bond as to put them on the same side, that would be another stereoisomer (specifically a diastereomer).

Finally, consider that for each possible configuration of chirality centers, there is a diastereomer of the double bond rotated in the previously described fashion.

Hence, we would have 8 possible stereoisomers.