4
$\begingroup$

The prefix "per-" appears in the names of many compounds, such as in perchlorate, persulfate, peroxide. What does it mean?

$\endgroup$
  • $\begingroup$ See my comment in the thread under my answer here. $\endgroup$ – Todd Minehardt Nov 9 '15 at 14:12
4
$\begingroup$

Per- can mean a number of different things, depending on the context. It can mean that there is a peroxi bond(oxygen-oxygen bond) in the system, persulfate is a good example of this.

More generally it tends to mean that the compound is the most completely altered product of a certain(possibly hypothetical) reaction. For example perchlorates and permanganates are the most completely oxygenated compounds of chlorine and manganese, respectively. This also describes another common use of per-, perhalogenated compounds. In that context, it usually means that all hydrogens present in the parent compound, that were bonded to a carbon, have been replaced with a halogen, for example perfluoroethylene (C2F4, also known as tetrafluoroethylene, the monomer of Teflon(PTFE))

$\endgroup$
  • 2
    $\begingroup$ According to current IUPAC recommendations, the prefix "per-" is no longer recommended for organic compounds in which all substitutable hydrogen atoms are completely substituted (e.g. perfluoroheptane). $\endgroup$ – Loong Nov 9 '15 at 1:45
  • $\begingroup$ @Loong are there substituting recommendations or must one say octadecafluoroheptane? $\endgroup$ – Jan Nov 9 '15 at 13:15
  • $\begingroup$ @Jan The preferred IUPAC name for perfluoroheptane $(\ce{C7F16})$ is hexadecafluoroheptane. Note that all locants are omitted, i.e. the name is not 1,1,1,2,2,3,3,4,4,5,5,6,6,7,7,7-hexadecafluoroheptane. $\endgroup$ – Loong Nov 9 '15 at 13:27
  • $\begingroup$ I came here looking for this compound - perfluorobenzene - which has all its hydrogens replaced by a halogen, am commenting if anyone else googles this as well. $\endgroup$ – Gaurang Tandon Jan 7 '18 at 16:17

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.