Hydrogen bonding in chloral hydrate

3,167

As noted in the comments, the fallacy is the notion that only a select few atoms can form hydrogen bonds with protic hydrogen. In reality, the strongest hydrogen bonds involve nitrogen, oxygen, or fluorine, but most nonmetals can form such bonds if they have an electron pair to donate to the bond. Hydrogen bonding with chlorine is seen in the $\ce{HCl_2^-}$[1], which is analogous to the more familiar bifluoride ion, as well as chlorine-bearing organic compounds[2].

References

1. Harry F. Herbrandson, Richard T. Dickerson Jr., and Julius Weinstein, " Cite this: J. AThe Bichloride Ion", J. Am. Chem. Soc. 1954, 76, 15, 4046. https://doi.org/10.1021/ja01644a066

2. R. Banerjee, G. R. Desiraju, R. Mondal, J. A. Howard. "Organic chlorine as a hydrogen-bridge acceptor: evidence for the existence of intramolecular O--H...Cl--C interactions in some gem-alkynols." Chemistry 2004 Jul 19; 10(14):3373-83. https://doi.org/10.1002/chem.200400003. PMID: 15252783.

3,167

SR.

Updated on August 01, 2022

Comments

SR. 10 months

Normally, chlorine doesn't form hydrogen bonds because despite its electronegativity, the size of the atom is such that its electron density is too low to form hydrogen bonds.

However, chlorine forms hydrogen bonds in chloral hydrate (2,2,2-trichloroethane-1,1-diol). What could be the possible reason for this?
- ParaH2 almost 5 years
  
  I am far from to be a specialist of organo-chemistry. However I remember learning that geminal diols are particularly unstable. So I would say maybe in this case the hydrogen atoms exhibit "a smaller electronic density" (the electrons are diffused in the whole molecular orbitals) then even the small electronic density of the chlorine atoms would be enough to get a very weak hydrogen bond.
- Mithoron almost 5 years
  
  Possible duplicate of Is hydrogen bonding generally defined to include only three period two elements?
- Mithoron almost 5 years
  
  In other words, your starting premise is false - Cl hasn't got much problem with hydrogen bonding. It's just weak. For some reason weak hydrogen bonds often aren't considered at all.
- pentavalentcarbon almost 5 years
  
  How is that a duplicate if chloral hydrate includes a $\ce{Cl\bond{...}H}$ hydrogen bond? Or is this a misconception?
- Mithoron almost 5 years
  
  @pentavalentcarbon it is misconception to be debunked. I couldn't find straight up dupe, but there as many posts about it.
- pentavalentcarbon almost 5 years
  
  @Mithoron Then that should be part of an answer. Closing a question because it contains a misconception is not right; closing should be indicating a question should be improved.
- Mithoron almost 5 years
  
  @pentavalentcarbon There is no problem with Cl in hydrogen bonds and this misconception was thoroughly debunked already.
Jon Custer over 4 years

Most chemistry is associated with thermodynamics!
Oscar Lanzi over 3 years

Hydrogen bonds are bonds! They involve the formation of molecular orbitals that produce a bonding overlap.