def inchi
      unless self["inchi"]
        result = obconversion(smiles,"smi","inchi")
        update(:inchi => result.chomp) if result and !result.empty?
      end
      self["inchi"]
    end
def inchi
      unless self["inchi"]
        result = obconversion(smiles,"smi","inchi")
        update(:inchi => result.chomp) if result and !result.empty?
      end
      self["inchi"]
    end
Get InChI
 @return [String]