I currently need to read a paper. In that paper the following compound was mentioned:


I tried to find the corresponding structural formula using the OPSIN parser at: http://opsin.ch.cam.ac.uk/ but I got the error message:

1,2-benzo-6-(N-ethyl-N-isobutylamino)fluoran was uninterpretable due to the following section of the name: 1,2-benz

I also tried just googleing the compounds name but the only thing I found where patents which weren't very useful.

I hope somebody can help me find the structural formula.

  • $\begingroup$ Do you have a link to the paper you found the compound in? Some context would be useful $\endgroup$
    – NotEvans.
    Jul 26, 2016 at 22:59
  • 1
    $\begingroup$ @NotNicolaou Yes. See Table 1 example 6. google.com/patents/US6494950 $\endgroup$
    – Jeanma
    Jul 26, 2016 at 23:14

1 Answer 1


The name given is not standard.

Fluoran itself is a spiro compound with two components:


(it's strictly an isobenzofuranone, but I'm lazy to type that multiple times.)

Because of the nomenclature rules of spiro compounds (which I'm sure someone will come along and tell you all about), the atoms in the benzofuran system are labelled 1-7 and those in the xanthene system are labelled 1'-10', with an apostrophe.

Atoms 1 and 2 of the benzofuran system are both within the furan ring. If I am not wrong, atom 1 is the carbonyl carbon, and atom 2 is the ring oxygen. The given name, that starts with "1,2-benzo", therefore makes no sense as you cannot fuse a benzene ring to atoms 1 and 2 of the benzofuran system.

After a little bit of Googling, I came across this compound: 6'-(Diethylamino)-1',2'-benzofluoran. I think with the apostrophes, it makes much more sense.

The numbering within the xanthene system parallels that of anthracene:


Having "1',2'-benzo" means that you have an additional fused benzene ring to carbons 1' and 2'. The 6'-substituent also makes sense. Chances are if the paper you were reading labelled the xanthene atoms with 1-10 without apostrophes, the 6-amino group should be a 6'-amino instead. Your desired structural formula is probably

Final compound

ChemDraw's name to structure generator gives this molecule when you input 6'-(N-ethyl-N-isobutylamino)-1',2'-benzofluoran. The amino group, which is just an ordinary substituent, should probably be a prefix to "benzofluoran" which is the parent compound.

I am sure in due time someone will come along and give you all the official IUPAC rules but I figured that if you just wanted the structural formula, my not-very-rigorous explanation would suffice.

  • $\begingroup$ There appears to be an (old) alternate convention where the benzofuran has the primes instead, which the source could be using. See page 560 in this proposal: fluoran (156) is listed at the bottom. $\endgroup$
    – f''
    Jul 27, 2016 at 0:18
  • $\begingroup$ If that is the numbering that is being used, then the "6-amino" group would be on the carbon now numbered as 5'. $\endgroup$
    – f''
    Jul 27, 2016 at 0:27
  • $\begingroup$ @orthocresol In view of similar structure formulas in Y. Hatano: The Chemistry of Fluoran Leuco Dyes and related patents, your interpretation of the name is probably correct. $\endgroup$
    – user7951
    Jul 27, 2016 at 11:15
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    $\begingroup$ By the way, the preferred systematic name of this compound is 9'-[ethyl(2-methylpropyl)amino]-3H-spiro[2-benzofuran-1,12'-benzo[a]xanthene]-3-one. However, a detailed explanation of this name would probably require at least one new question. $\endgroup$
    – user7951
    Jul 27, 2016 at 19:05

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