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

Question

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

Elias Aguila · Accepted Answer

Consider the molecule you describe,

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.

Elias Aguila · Answer

undefined To determine the number of stereoisomers of 2-chloro-5-fluoro-3-hexene, we first identify the chiral centers in the molecule. In this case, there is only one chiral center, which is the carbon atom bonded to the chlorine atom.

When a double bond is present in a molecule, it restricts the rotation around the bond, leading to cis-trans isomerism. However, in this molecule, the double bond is not involved in the chiral center, so it does not contribute to the number of stereoisomers.

For a molecule with one chiral center, the number of stereoisomers is determined by 2^n, where n is the number of chiral centers. In this case, n = 1, so the number of stereoisomers is 2^1 = 2.

Therefore, there are 2 stereoisomers of 2-chloro-5-fluoro-3-hexene.

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