Answer
1 - Br
2 - Cl
3 - (Right) Carbon
4 - (Left) Carbon
Work Step by Step
1. Identify the stereocenter.
2. List all atoms connected to the stereocenter, and rank them by the atomic number.
- Br, Cl, C, C
Ranked by atomic number:
- Br, Cl, C, C
3. As we can see, there are 2 equal atoms, and there are two methods for finding their order.
First Method (Faster):
- Find the closest variation in the chain (Double bond, Substituent).
- The chain with the closer variation gets priority.
In this case the right chain has a double bond, so the right carbon gets priority.
Second Method:
- Compare the atoms connected to each carbon, and if you don't get the answer, then look at the atoms connected to them.
In this case:
Already ranked by atomic number:
Left Carbon: C, H, H
Right Carbon: C, H, H
They are equal, so we will proceed to compare these new 2 carbons.
Second Left Carbon: C, H, H.
Second Right Carbon: C, C, H.
** If there is a double bond, we count the atom connected 2 times.
- Since (C>H), the Second Right Carbon gets priority, therefore, the Right Carbon gets priority.
4. Put the numbers on the stereocenter atoms:
1 - Br
2 - Cl
3 - (Right) Carbon
4 - (Left) Carbon
