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Question: says that1:

...in reality, p-chlorobenzoic acid is less acidic than p-fluorobenzoic acid . Why?

I checked the $\mathrm{p}K\mathrm{a}$ values, and they are:

So, 4-chlorobenzoic acid is indeed more acidic than 4-fluorobenzoic acid. Yet, currently this question has three answers and a +8 score! (all supporting the "fact" that 4-chlorobenzoic acid is less acidic than 4-fluorobenzoic acid2)

I checked this meta discussion, I agree that "debunking a myth" is very important. But, the above question is not a myth. There is clear data that 4-chlorobenzoic acid is more acidic, and it took me just one google search to find it.

Now, my question is, what do we do of this question? It has 301 views, so it's not very popular, but we still need to do something. I do not know what action will be the best, hence, it is time for the community to discuss.


1: I agree that I was the one who actually inserted that sentence yesterday (when I had yet not checked the pKa values) But, even if you go to the earliest revision, the basis of the question is still the same: "...para substituted fluorine should be less acidic...point to benzoic acid with para substituted chlorine being more acidic....However, this is not the case. Why?"
2: Except Soumik Das, who correctly answers that "acidity of 4-chlorobenzoic acid is little higher than that of 4-fluorobenzoic acid."

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  • $\begingroup$ Just edit it , it's a question from last year and the OP isn't active anymore.. $\endgroup$ – Avnish Kabaj Feb 24 '18 at 15:37
  • $\begingroup$ @AvatarShiny "Just edit it" and invalidate both the other answers already posted+the eight upvotes the question received? $\endgroup$ – Gaurang Tandon Feb 24 '18 at 15:39
  • $\begingroup$ Well wrong answers aren't valid anyway and how does it matter upon how many upvotes a question got correct questions matter. $\endgroup$ – Avnish Kabaj Feb 24 '18 at 15:40
  • $\begingroup$ @AvatarShiny If anyone suggested such an edit to this question, I would reject it on the grounds of "clearly conflicts with the author's intent". I am sorry but I do not feel comfortable doing what I would reject myself. $\endgroup$ – Gaurang Tandon Feb 24 '18 at 15:41
  • $\begingroup$ @AvatarShiny "What is the point of this question?" To bring the community's attention towards an invalid question that remained open for so long without anyone noticing the false information here, and to now decide the best way to handle this question. If you consider your approach to be the best, please post an elaborate answer and let the community decide. $\endgroup$ – Gaurang Tandon Feb 24 '18 at 15:44
  • $\begingroup$ I feel like this suggested edit keeps the author's intent intact and deals with the issue. $\endgroup$ – Avnish Kabaj Feb 24 '18 at 23:25
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I don't think that this case presents any kind of different situation than that previously outlined in I'm voting to close this question as off-topic because it's based on false premise.

I checked this meta discussion, I agree that "debunking a myth" is very important. But, the above question is not a myth. There is clear data that 4-chlorobenzoic acid is more acidic, and it took me just one google search to find it.

I would say that there is equally as much clear data, that d-orbitals have no significance in so called "hypervalent" [sic] compounds.
I would still always argue in favour of keeping such questions open, and answer them so that these false information gets debunked.
There really is no difference here, because the question is coming from somewhere, and leaving it unanswered, it might come up again. Even worse if it is closed, because then it sticks around and spreads like a disease, as maybe, probably being true; I wouldn't want to shoulder that burden.

Now, my question is, what do we do of this question? It has 301 views, so it's not very popular, but we still need to do something. I do not know what action will be the best, hence, it is time for the community to discuss.

You do what you always do: vote. And comment. And answer.
There really is nothing which needs to be done from an "official capacity" (be it mods or community consensus), but especially closing it would be an absolute false sign to send from my point of view.

The very best way to deal with these questions it to answer them, stating that it is based on wrong data/ a misconception/ an error, correct that factoid and explain it. (Everything else feels like policing content here to me.)

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  • $\begingroup$ I'd +1 for "I would say that there is equally as much clear data, that d-orbitals have no significance in so called "hypervalent" [sic] compounds." haha :P I am still unsure how this false information even came up about in the first place, though. At least, pKa tables are much easy for high schoolers to check than d-orbital contributions :/ tl;dr: I'd downvote it. The OP should've checked the pKa tables. $\endgroup$ – Gaurang Tandon Feb 26 '18 at 5:33
  • $\begingroup$ @Gaurang I actually find the initial question clear, sure, more research would have been nice, but then again I would not consider these acids very different in the first place. I am pretty sure that in the pKa tables I had in school, these compounds would not have shown up. And in case you don't know that about me yet, I judge questions entirely on how interesting and useful I find them; for this case, the values wouldn't have changed that, and the opposite premise neither. $\endgroup$ – Martin - マーチン Feb 26 '18 at 5:47
  • $\begingroup$ Okay, I might need some time to see this situation through a different context, and to be able to digest your point of view. This is new for me. $\endgroup$ – Gaurang Tandon Feb 26 '18 at 12:09
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Just adding the $\mathrm pK_\mathrm a$ values will not be conflicting author's original intent as they are simply facts.
I would prefer if a disclaimer note was also included in the edit as that would clear up any confusion.

Something along the lines of

OP's statement conflicts with the pKa values.

Currently my proposed edit is:

However, in reality, p-chlorobenzoic acid is less acidic than p-fluorobenzoic acid. Why?


  • $\mathrm pK_\mathrm a$ of para chlorobenzoic acid $\to 4.03$.Source

  • $\mathrm pK_\mathrm a$ of para fluorobenzoic acid $\to 4.14$.Source

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  • $\begingroup$ I am not really sure how this will solve the problem. It just makes the question self-contradictory - "p-chlorobenzoic acid is less acidic than p-fluorobenzoic acid...[insert pKa values]look at these pKa values, they suggest the opposite fact!" $\endgroup$ – Gaurang Tandon Feb 25 '18 at 2:07
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I wish to close this question as "unclear what you're asking".

It really does not make any sense what the OP is trying to ask. The OP based his entire question on "p-chlorobenzoic acid is less acidic than p-fluorobenzoic acid" but the pKa values suggest that the reverse fact is true. So, what was the OP even trying to ask in the first place? Make us prove a "fact" that is untrue?

I am not sure if anything can be done about the answers that have already been posted, but, I don't have any better idea right now. If you have a better idea, please post it; else, upvote this one! ;)

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