text: The thionyl group is SO, a sulfur atom plus an oxygen atom.
  It occurs in compounds such as thionyl fluoride, SOF.
  Thionyl chloride, SOCl, is a common reagent used in organic synthesis to convert carboxylic acids to acyl chlorides.
  In organic chemistry, the thionyl group is known as a sulfoxide group or sulfinyl group, and has the general structure RS(=O)R'.