The Hydrogen Bond in the Solid State

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The Hydrogen Bond in the Solid State
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Introduccion

• It is pertinent to recall here the earlier
  classical view on hydrogen bonding. One may
  consider the directional interaction between
  water molecules as the prototype of all hydrogen
  bonds.

The dissociation energy is around 3 ? 5 kcalmol
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• This brief outline of the hydrogen bond between
  water molecules can be extended with only minor
  modifications, to analogous interactions .

We know of hydrogen bonds that are so strong that
they resemble covalent bonds in most of their
properties, and we know of others that are so
weak that they can hardly be distinguished from
van der Waals interactions
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Fundamentals

• Early definition is that of Pimentel and
  McClellan, who essentially wrote that ...a
  hydrogen bond exists if
• 1) there is evidence of a bond, and
• 2) there is evidence that this bond sterically
  involves a hydrogen atom already bonded to
  another atom

For crystalline compounds, it is easy to see with
diffraction experiments whether an H atom is
involved, but it is difficult to guarantee that a
given contact is actually bonding.

1. An interaction is called a hydrogen
   bond?, if
2. it constitutes a local bond, and
3. acts as proton donor to A.

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In a hydrogen bond XH A, the group XH is called
the donor and A is called the acceptor
Some authors prefer the reverse nomenclature (XH
electron acceptor, Y electron donor), which is
equally justified
Bifurcate Centered which is the term preferable
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The schematic hydrogen bond potential in Figure 1
shows that a stabilizing interaction (that is,
with E0) is associated with a repulsive force if
it is shorter than the equilibrium distance (see
figure legend for further details)?
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Energies
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Geometry
Donor Directionality
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Donor Directionality
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Acceptor Directionality
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Distributions and Mean Values of the HA Bond
Lengths
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