The Potential within H-bonds

[HydrogenBond]

Hydrogen bonds are more than a dipole potential between a hydrogen atom and the unbonded electrons of an highly electronegative atom. What makes hydrogen bonds unique is that the hydrogen goes into the hydrogen bond carrying the primary burden of the potential. The shared electrons will have a lower potential to form the hydrogen bond.

 

This can be understood by looking at the hydrogen bonding in water. A water molecule will have four hybrid sp3 orbitals. The hydrogen of water are bonded to two of these four orbitals. The other two hybrid orbitals have the two pairs of unshared electrons that participate in hydrogen bonding.

 

The hybrid orbitals allow hydrogen to share electrons with the oxygen, but at a higher orbital distance due to the P-character of the hybrid orbitals. In other words, hydrogen is optimized for 1S orbitals, but is induced by the bond with oxygen to share electrons with a lot of P-character. This sort of ionizes the electrons shared by hydrogen away from is 1S orbital. It has electron density to balance most of its positive charge, but it is being held further away from its 1S orbtal than is optimum.

 

The oxygen, on the other hand, gains the electron density to become slightly negative, but these electron are placed in hybrid orbitals more in line with the p-orbital needs of oxygen. As such, although the charge dipole will balance, the hydrogen has a higher overall potential.

 

Data that supports this is connected to hydrogen bond energy dropping drastically with deviation from linear hydrogen bonding angles. In other words, if we maintain the distance between the hydrogen and shared electrons within the hydrogen bond, but only shift the angle, this should not affect an electrostatic attraction. The angle deviation has more to do with lining up orbitals. The linear arrangment allows the hydrogen to compensation for its p-character ionization by allowing it to share some of the p-character of the unbonded electrons. If we shift the angle, the lower hydrogen bond energy becomes more dependant on electrostatic attraction.

 

Another supporting observation is the contraction of water when it melts. The only other material in nature that does this is the metal Antimony. When water is ice the hydrogen bonds are linear and the potential of the hydrogen is minimized due to the p-orbital sharing with the unbonded electrons. When we heat ice and cause it to melt, the oxygen is able to twist away. This alters the angle causing the lower potential electrostatic force to have get much closer to lower potential.

 

In liquid water the hydrogen would like to line up the oxygen but often as to settle for electrostatic attraction. This causes hydrogen to maintain some residual or orbital based potential. The extra potential left in the hydrogen of liquid water, ionize metallic electrons, catalyzing oxidation. In other words, metals will corrode much faster in low oxygen solubile water, than in high oxygen soluble dry air, due to the potential of the hydrogen of water acting as a catalyst.

[HydrogenBond]

The lopsided potential with hydrogen bonding hydrogen, especially those connected to oxygen and nitrogen are important because they open up a whole new branch of bio-physical chemistry. The living state is based on hydrogen bonding. The DNA, RNA, Proteins and water of the cell are all dependant on hydrogen bonding to define their properties. The little extra in the hydrogen bonding hydrogen, theoretically allows one to model the cell in term of one variable, i.e., hydrogen bonding potential.

 

Just as the electron and orbitals are sufficient to define all of molecular chemistry, the hydrogen bonding hydrogen is sufficenct to define the living state. In other words, hydrogen bonding is another layer onto top of the electrons and orbtials. All the complex chemistry of life is there for the integrated workings of the hydrogen proton.