Chemical Forums
Chemistry Forums for Students => Inorganic Chemistry Forum => Topic started by: AlbertoA on August 19, 2011, 08:29:58 PM
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Can the molecules of HCl can form a Hydrogen bond? and Why?
PLEASE don't say answers like "HB can only exist in X-H -- X where X is O, F or N"
I've read a new definition in a book, i don't remember the author, but it bassically says that and HB is formed when an electronegative atom is bonded with a H, so the H will have a partial positive cahrge allowing HB with the other electronegative atom... I think I read it in "Inorganic chemistry" by Housecroft
Also, does C-H --- O exists?
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Let me answer your question about C-H---O first : There is no hydrogen bonding here. For H-bonding, as you have probably already read, you need a partial positive charge on the H. But the electronegativity difference between C and H is too less for any kind of substantial partial positive charge development on H. Hence the negatively charged (partial) oxygen cannot get hydrogen bonded to the C-H hydrogen.
This charge separation is substantial in the case of F, N and O. i.e, if the H is bonded to these. So, F-H---F, O-H---O, N-H---N, O-H---F, O-H---N, (and all the other permutations) are considered to be hydrogen bonded ones.
HCl is not hydrogen bonded, although there is a good amount of dipole-dipole attraction. Due to the size of Cl, this interaction is weaker than the usual H bonds.
Hope my explanation was clear.
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Let me answer your question about C-H---O first : There is no hydrogen bonding here. For H-bonding, as you have probably already read, you need a partial positive charge on the H. But the electronegativity difference between C and H is too less for any kind of substantial partial positive charge development on H. Hence the negatively charged (partial) oxygen cannot get hydrogen bonded to the C-H hydrogen.
This charge separation is substantial in the case of F, N and O. i.e, if the H is bonded to these. So, F-H---F, O-H---O, N-H---N, O-H---F, O-H---N, (and all the other permutations) are considered to be hydrogen bonded ones.
HCl is not hydrogen bonded, although there is a good amount of dipole-dipole attraction. Due to the size of Cl, this interaction is weaker than the usual H bonds.
Hope my explanation was clear.
Even if the Cl is more electronegative than N? how does size matter? because.. the partial negative charge would be spread out in a larger surface?
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Yes. Charge density is important.
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Let me answer your question about C-H---O first : There is no hydrogen bonding here. For H-bonding, as you have probably already read, you need a partial positive charge on the H. But the electronegativity difference between C and H is too less for any kind of substantial partial positive charge development on H. Hence the negatively charged (partial) oxygen cannot get hydrogen bonded to the C-H hydrogen.
This is true, but I'd like to point out that C-H---X hydrogen bonds do exist in cases where the substituents on the carbon are sufficiently electron withdrawing. :)
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You mean something like F-C-H---F? F being electronegative.... ?
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You mean something like F-C-H---F? F being electronegative.... ?
I would hesitate to generalize it in that way. Maybe C-H---X where the substituents on the C drawn significant electron density off the H, and X has sufficient electron density to accept the hydrogen bond.
Chloroform can be involved in hydrogen bonding as a C-H hydrogen bond donor for example. Other examples are out there too. I did a quick search on ACS and found a example (http://dx.doi.org/10.1021/cg060806w) where CC-H---N hydrogen bonding creates a two-dimensional network.