Quick simple H-bonding question

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In summary, the presence of a hydrogen directly bonded to a highly electronegative element, such as N, O, or F, is typically required for hydrogen bonding to occur in a molecule. However, in some cases, such as with formaldehyde and possibly acetal, hydrogen bonding may still occur even if the hydrogen is not directly bonded to the electronegative element. This can be due to factors such as local dipole moments and the hydrogen's donor/acceptor capabilities.
  • #1
bomba923
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*Must a hydrogen be 'directly' bonded to an N,O, or F in the very structure of the molecule for it to engage in H-bonding with other such molecules?

*For example, can formaldehyde form H-bonds? --even though its hydrogens are not directly bonded with an oxygen in the structure? (i.e., not structurally attached) What about acetone or acetal?

*Or, must I concretely have an (O-H) or (N-H) bond within the molecule structure itself?

So, must a hydrogen be 'directly' bonded to an N,O, or F in the very structure of the molecule for it to engage in H-bonding with other such molecules?
 
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  • #2
Taken from

http://www.chemguide.co.uk/atoms/bonding/hbond.html

:

"In methoxymethane, the lone pairs on the oxygen are still there, but the hydrogens aren't sufficiently + for hydrogen bonds to form. Except in some rather unusual cases, the hydrogen atom has to be attached directly to the very electronegative element for hydrogen bonding to occur."
 
  • #3
Artermis said:
. .. Except in some rather unusual cases, the hydrogen atom has to be attached directly to the very electronegative element for hydrogen bonding to occur .. ..

Meaning formaldehyde, and possibly acetal, I presume ? :smile:
Not acetone?
 
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  • #4
Yeah, it's not a clear cut case. You're first assumption is correct in most cases, the hydrogen has to be bonded to the electronegative atom, this pertains to a local dipole moment due to the direct electronegative differences, which will facilitate intermolecular attractions so deemed to be hydrogen bonding.

You should also consider the scenario of hydrogen donor/acceptor capabilities when considering the nature of hydrogen bonding in a system.

And as artemis has mentioned there are cases where the partial charge differences between two hydrogen bonding candidates can be "stabilized" by hyperconjugation of electron donors and such.
 

1. What is a hydrogen bond?

A hydrogen bond is a type of intermolecular bond between a hydrogen atom and an electronegative atom, such as oxygen, nitrogen, or fluorine. It is a weaker bond compared to covalent or ionic bonds, but it still plays an important role in many biological and chemical processes.

2. How does hydrogen bonding occur?

Hydrogen bonding occurs when the positive end of a polar covalent bond (hydrogen) is attracted to the negative end of another polar covalent bond (electronegative atom). This creates a partial electrostatic attraction between the two molecules.

3. What are some examples of molecules that can form hydrogen bonds?

Water, ammonia, and hydrogen fluoride are some common examples of molecules that can form hydrogen bonds. Other examples include DNA base pairs, alcohols, and carboxylic acids.

4. How does hydrogen bonding affect the properties of molecules?

Hydrogen bonding can affect the properties of molecules in several ways. It can increase the boiling and melting points of molecules, as well as their solubility in water. It can also affect the shape and structure of molecules, such as in the case of DNA.

5. Can hydrogen bonding occur between any two molecules?

No, hydrogen bonding can only occur between molecules that have a hydrogen atom bonded to an electronegative atom, and another electronegative atom available to form a bond. This is why not all molecules are capable of forming hydrogen bonds.

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