HFC-1234yf HFC-365mfc

[AastroGuru]

I understood the numbering part of HFC-1234yf or HFC-365mfc.

But what is the procedure to write the alphabets 'yf,' 'mfc' etc.,

example
----F---F---H
----|---|---|
F - C - C = C
----|-------|
----F-------H

This gives HFC-1234
1> one unsaturateed carbon - carbon bond
2> three carbon atoms -1
3> two hydrogen atoms +1
4> four fluorine atoms
this makes 1234.

How to determine 'yf'

For simple substances like HFC-225ca i understand how ca is determined.
c - denotes decreasing order atoms attached to central carbon atom
a - based on side carbon atoms


I didnt have ASHRAE Standard 34. I cant afford $37. Please help.