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Why can't chlorine atoms form hydrogen bonds even though they have very similar electronegativity to nitrogen, which can?

Electronegativities are as follows:

$\ce{Cl} - 3.16$

$\ce{N} - 3.04$

Is it because of the size ?

  • The existence of hydrogen bonds involving chlorine atoms was disputed a while ago, but experimental data show that chlorine atoms can form hydrogen bonds, and are in fact very common. See C.B. Aakeröy et al., The C–H···Cl hydrogen bond: does it exist? New J. Chem., 1999,23, 145-152. DOI: 10.1039/A809309A – vapid Oct 20 '16 at 07:08
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    I really hate to do that, but quora actually has a good answer on that. (a as in one, only one good answer, i.e. the one by by Mario Barbatti) find it here – Martin - マーチン Oct 20 '16 at 08:39
  • also related: http://chemistry.stackexchange.com/q/5503/4945 – Martin - マーチン Oct 20 '16 at 08:40
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    and here is real answer http://chemistry.stackexchange.com/questions/21773/why-is-hydrogen-bonding-generally-defined-to-include-only-three-period-two-eleme – Mithoron Oct 20 '16 at 10:13
  • If I wanted to close, I'd rather close as the latter. @Mith Anyway, I will let you guys decide... – orthocresol Oct 20 '16 at 10:33
  • Yeah, probably second one is better. – Mithoron Oct 20 '16 at 10:51
  • This discussion is really dubious. I would be careful about saying that chlorine engages in hydrogen bonds and argue with e.g. Cl-H-Br hydrogen bonds. Hydrogen bonds are mainly interesting in a biological context and then there are no chlorine hydrogen bonds. Even if there are chlorine bromine hydrogen bonds when you stir fuming HCl in a magic acid mixture at 400°C this doesn't mean that they occur in real world scenarios as well. Show me one protein where a Cl h.-bond occurs and I am convinced. $\mathrm{Cl^-}$ is just not basic enough to engage in significantly strong hydrogen bonds. Period. – logical x 2 Oct 20 '16 at 15:32
  • @ketbra Seems you're not accepting the existance of weak H-bonds. All this N,O,F stuff are moderately or very strong examples but there can be weak or even very weak ones and they are also important, for example in protein folding. – Mithoron Oct 23 '16 at 20:52
  • @Mithoron Than could you please give an example where Cl is important in protein folding? – logical x 2 Oct 23 '16 at 23:09
  • General stuff about weak H-bonds: http://pubs.rsc.org/en/content/articlepdf/2000/CC/A900221I Halogens in hydrogen bonds: http://pubs.acs.org/doi/pdf/10.1021/cg015522k#page=8&zoom=auto,-99,758 – Mithoron Oct 24 '16 at 23:43

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