Question

What is stereo structural IUPAC name of the following compound?

Answer 1

The name of the compound is (`2S,3R`)-2-bromo-3-chloropropane.

Explanation:

Configuration at `"C-2"`

The Cahn-Ingold-Prelog priorities of the groups on `"C-2"` are

`"Br = 1; C-3 = 2; C-1 = 3; H = 4"`

The `"H"` atom is furthest from our eye, and the 1 → 2 → 3 direction is counterclockwise.

Thus, the configuration at `"C-2"` is `S`.

Configuration at `"C-3"`

The Cahn-Ingold-Prelog priorities of the groups on `"C-3"` are

`"Cl = 1; C-2 = 2; C-4 = 3; H = 4"`

The `"H"` atom is closest to our eye, and the 1 → 2 → 3 direction is counterclockwise.

The configuration at `"C-3"` appears to be `S`.

However, because the `"H"` atom is closest to our eye, we invert the assignment.

The configuration at `"C-3"` is `R`.

The name of the compound is, therefore, (`2S,3R`)-2-bromo-3-chlorobutane.

NOTE:

Your image was the PubChem structure for (`2S,3S`)-2-bromo-3-chloro-butane.

They give three structures.

Wedge-Dash

(From PubChem)

This is the (`2S,3S`) isomer.

Wire Frame

This is the structure you give.

Amazingly, PubChem is incorrect. This is the (`2S,3R`) isomer.

3-Dimensional

(From PubChem)

This is the correct (`2S,3S`) structure.