what is the difference between home and auto freon?

To answer that you have to understand the properties of the dozens of different formulations of freon.  There is technically no such thing as "home" or "auto" freon.  Different refrigerants are formulated for different purposes based on the operating characteristics such as how much pressure they must be under to achieve their functional cooling capabilities.  They also must be able to "blend" with the types of oil needed to lubricate the internal components of the system.  The size of the system is crucial as well as the temperatures it must work under to perform its duty.  I could go on for hours, but the bottom line is you cannot mix them nor are they interchangeable.  Hope this helps.

Basically chemical structure and (consequently, since I'm a chemist) physical properties.  Both contain the elements carbon and one or more different halogens (chlorine, fluorine, bromine) or hydrogen.

Until the 1980s, the most widely used refrigerants were the halomethanes R-12 and R-22.  R-12 being more common in automotive air conditioning and small refrigerators and R-22 being used for residential and light commercial air conditioning, refrigerators, and freezers.

Some very early systems used R-11 because its low boiling point allows low-pressure systems to be constructed, reducing the mechanical strength required for components. New production of R-12 ceased in the United States in 1995, and R-22 is to be phased out in 2010. R-134a and certain blends are now replacing chlorinated compounds. One popular 50/50 blend of R-32 and R-125 now being increasingly substituted for R-22 is marketed under the trade name Puron®.