The time is ripe for a short chemistry quiz. In fact, a very short one – it’s only one question long. We used to traumatize undergraduates with this one towards the end of the first organic chemistry lab course. I can’t remember if a student ever got it right, and I’m certainly not sure whether it was correct to use this example, from a pedagogical point of view, as the correct answer when disclosed typically resulted in total confusion with the poor newcomer to the field. To my defense, we never used it on the final exam.

Let’s cut to the chase. Familiarize yourself with compounds 1 and 2; one is a thiophene and the other a benzene.


In what respect are the two compounds identical?

Hint #1: Nope, it’s not the molecular formulas. C4H4OS ≠ C6H6S

Hint #2: I’m well aware that the main tautomer of 1 is the keto-form. For this to work however, compound 1 has to be drawn in this way.

The first person who provides the correct answer in a comment below will receive an autographed copy of my thesis (sent anywhere in the world). I know it’s not much. That’s what I can afford to lose for the time being. Its value is negligible in comparison to this edition.

Anyways… good luck!

UPDATE: Jesus H. Christ, that was quick! 20 minutes after posting, two prominent readers submitted the winning answers almost at the same time. The answer is “thiophenol”. (Thiophen-ol vs. thio-phenol.) Congrats!


10 Responses to Quiz time!

  1. Chris says:

    Planar and aromatic

    • drfreddy says:

      Not untrue. But not spot on. Keep going. There is something very specific that is IDENTICAL between these two, and no other compounds.

  2. Ed says:

    Same Name? Thiphenol and Thiophen-(2)-ol ?

  3. Ben says:

    compound 1 – thiophene-ol
    compound 2 – thiophenol

    spelt differently but pronounced the same?

  4. drfreddy says:

    GEE… that was quick.

    Ben and Ed, check my email address under “About the author” and I’ll ship the prizes, if you’re interested.


  5. SiO2lungs says:

    how different are their pKa’s?

  6. Alex says:

    Shouldn’t that be hydroxythiophene? (provided enol tautomer)

    • drfreddy says:

      If we call them 2-hydroxythiophene and mercaptobenzene, this little quiz indeed falls apart.

      I have seen “thiophenol” being used to describe both 1 and 2 in papers. Perhaps this is not what IUPAC recommends in either case, but…

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