Who knows how many isomers of octafluorochlorobutane exist? ! ! !

Upload a picture to explain the idea of solving the problem:

1, f is no longer marked, because it is f except Cl;

2. Two kinds of carbon skeleton, the upper six are straight chains and the lower three are branched chains;

3. The first four are carbons with terminal groups connected to Cl; The middle two are terminal carbons without Cl;

4. Black dots are asymmetric carbon atoms. If you haven't learned them, please ignore them.

5. If asymmetry is not considered, there are nine kinds. If asymmetry is considered, there are twelve kinds of optical isomers.

6. If you have learned the concept of equivalent substitution, this problem is very simple. If you haven't learned it, you can draw hard according to the above ideas.