What is stereo structural IUPAC name of the following compound?

Feb 28, 2017

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

Explanation:

Configuration at $\text{C-2}$

The Cahn-Ingold-Prelog priorities of the groups on $\text{C-2}$ are

$\text{Br = 1; C-3 = 2; C-1 = 3; H = 4}$

The $\text{H}$ atom is furthest from our eye, and the 1 → 2 → 3 direction is counterclockwise.

Thus, the configuration at $\text{C-2}$ is $S$.

Configuration at $\text{C-3}$

The Cahn-Ingold-Prelog priorities of the groups on $\text{C-3}$ are

$\text{Cl = 1; C-2 = 2; C-4 = 3; H = 4}$

The $\text{H}$ atom is closest to our eye, and the 1 → 2 → 3 direction is counterclockwise.

The configuration at $\text{C-3}$ appears to be $S$.

However, because the $\text{H}$ atom is closest to our eye, we invert the assignment.

The configuration at $\text{C-3}$ is $R$.

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

NOTE:

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

They give three structures.

Wedge-Dash

(From PubChem)

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

Wire Frame

This is the structure you give.

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

3-Dimensional

(From PubChem)

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