I am a student studying basic organic chemistry (isomerism) and was asked a question to find the number of aromatic isomers of $\ce{C7H8O}$.In fact this was a question in IITJEE exam. So I tried to draw all and I found all but the problem is that I found more than all. The answer to the question is 5 which may be wrong(I don't know) but several websites state this. Here are some links to those:

Here is the list of isomers I found:

enter image description here

So what is wrong with the list of my isomers?

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    $\begingroup$ Obviously, by the author's intention, you were not supposed to think of furanes. $\endgroup$ Sep 3 at 9:49
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    $\begingroup$ "Actual answer" is a social construct. $\endgroup$ Sep 3 at 10:00
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    $\begingroup$ I mean, some people say something, and others say otherwise, and it all boils down to some subtlety in the definitions, and then someone brings up the three-membered rings, and chaos ensues. $\endgroup$ Sep 3 at 10:06
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    $\begingroup$ True, but you were not supposed to know all of chemistry while answering this. Setting the educational issues aside, your answer is more correct than the author's, but then again, three-membered things actually do exist, don't they? $\endgroup$ Sep 3 at 10:16
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    $\begingroup$ Piling on: 2-prop-1-enylfuran pubchem.ncbi.nlm.nih.gov/compound/53915682 and there are plenty more down this avenue $\endgroup$ Sep 3 at 23:02

You are completely correct - the furan derivatives you've drawn display unquestionable aromatic character, though the "strength" of their aromaticity is somewhat lower than various other prototypical organic aromatic compounds.

By aromatic, the examiners really were assuming you would think benzenoid. While the latter term is more precise for the intended purpose (evaluation of fundamental organic chemistry structural knowledge), it is also rather technical and somewhat obscure. However, most people with a high-school understanding of chemistry are not likely to consider more complex aromatic systems in a testing environment with time constraints, and so these terms are often used as very crude synonyms.

In a more general sense, consider that university entrance exams require thousands of variations of simple questions to be churned out every year, and there's only so many mistakes/oversights that quality control can pick up on. These questions are also designed to be read and answered in a handful of minutes. This leads to a lot of "lossy compression" and corruption of meaning, where subtleties in content are overlooked, intentionally or unintentionally. If you're looking at exam answer sheets as the ultimate dictators of truth, then you're doing it wrong, as Ivan pointed out.

But ultimately, good job for looking at the finer print!

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    $\begingroup$ I can draw a dozen more isoners with a furan ring, and I haven't even counted what can be made with a cyclopropenone ring. Please do not attempt to formulate problem statements when drinking the real Budweiser beer from the Czech Republic! $\endgroup$ Sep 3 at 18:33

I just wanted this question not to be unanswered when the answer was itself subtly discussed in the comment section. Hence here's the part of discussion which provides some answer to this question. Of course the knowledge was borrowed and this is from @IvanNeretin .

Ivan Neretin emphasizes the flexibility of answers and the social structure of education. Hence for the needs of basic education, the question only includes 5 isomers which include benzene as the core but the "more" correct answer should be the structures I drew. And according to @Waylander, there are at least two more isomers available for the formula which are 3-cyclopropylfuran & 2-cyclopropylfuran. @Martin also states that that there are several other isomers missing of which he gives one example 2-prop-1-enylfuran .

Thanks to Ivan Neretin and all others for their help and time.


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