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Why don't carboxylic acids form H-bonds in this formation with the red dots (diagonal) instead of the black dots (horizontal)?

carboxylic acid hydrogen bonding scenarios

I was always taught that H-bonds formed between partially negative and partially positive atoms. I agree that the $\ce{=O}$ carboxyl oxygen is partially negative, so there should be a H-bond there from the partially positive H.

However, the $\ce{O}$ in $\ce{OH}$ is also partially negative. So why aren't the H-bonds denoted with red dots formed?

andselisk
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John Hon
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    And nobody told you that it goes straight to lone pair? – Mithoron Jul 29 '20 at 13:55
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    So, while bifurcated hydrogen bonds do exist, it's not the case here. – Mithoron Jul 29 '20 at 15:53
  • Does the red-dotted line from the hydrogen lead to electron pairs on oxygen? I think not. – user55119 Jul 29 '20 at 16:04
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    You need some degree of orbital overlap. Pretty challenging to overlap at that kind of angle. – Josh Mitchell Jul 29 '20 at 16:08
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    In reality in carboxylic acids, there are no double bond and single bond on oxygens. It is a hybrid (e.g., where is the $\ce{^{13}C}$-signal for carboxylic carbonyl in NMR?). – Mathew Mahindaratne Jul 29 '20 at 17:52
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    Often times you ignore the stuff that is not as important. It's a simple cartoon after all. – Buck Thorn Jul 29 '20 at 20:34
  • @MathewMahindaratne Isn't that just an issue with fast exchange in NMR? I would think that the oxygens are inequivalent (in a carboxylic acid in general; in the picture shown here for paired groups the inequivalence of the oxygens is less clear). – Buck Thorn Jul 29 '20 at 20:39
  • H-bonds are indeed bonds, and your black dotted lines give a 6-ring, and with the red, it´s a 4-ring. If you want to know for sure, check the crystal structure of any carboxylic acid. – Karl Jul 30 '20 at 06:25
  • @Mithoron but isn't there a lone pair on the red bond oxygen? – John Hon Jul 31 '20 at 00:23
  • And what does "straight to" mean? - Lone pair is no the other side of oxygen. – Mithoron Jul 31 '20 at 15:33
  • https://chemistry.stackexchange.com/questions/60640/why-cant-alcohols-form-hydrogen-bonded-dimers-like-carboxylic-acids – Mithoron Jul 31 '20 at 20:15

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