Add Column in order to separate data from existing column

Hi,

I am trying to separate data in a column that can appear in the original column with or with or without delimiters.

Example 

Each of the below representssome of the potential entries in original column by row:

[string 1, string 2, string 3]

[string 2, string 4, string 5]

[string 1, String 2, string 4, string 5, string 7]

[string 1]

[string 2]

Because the delimiter could be present or not the eliminates the possibility of extraction using a delimiter, because the strings don't always appear in the same order, that eliminates extracting by chatacters. I tried adding a conditional column, maybe I entered that incorrectly but it errored out on me.

There are null values in the column but if in my conditional operator using contains string2, then return string2, else blank, I was thinking that should work, and I can't understand why it isn't working. 

I appreciate any help you can provide.

Thanks,

Amber