Question

What is the E-Z designation of the following compound?

Answer 1

That is based on the Cahn-Ingold-Prelog (CIP) nomenclature priorities.

And we would get the `E` isomer.

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You would consider:

1. Atomic number of the first atoms around the stereocenter
2. Going one atom out if there is a tie
3. Treating multiple bonds as "ghost atoms" in further single-bond branching

In this case, all of these first atoms around the stereocenter are different atomic number. So we only need to consider rule 1 to get:

• Priority 4 = `"C"_6"H"_5`
• Priority 3 = `"CH"_3"NH"`
• Priority 2 = `"Br"`
• Priority 1 = `"I"`

Then, you divide the molecule in two, bisecting the double bond. This gives a higher priority on `"I"` on the right half and `"CH"_3"NH"` on the left half.

Since `"CH"_3"NH"` and `"I"` are the highest priority on their respective sides of the molecule, this is the `color(blue)(E)` isomer, as they are trans to each other.