Hydrogen Bonding and Its Effects
From the Simple Changes to Protein Folding and the Double Helix of Life
Description
A hydrogen bond is the electrostatic attraction between an atom of hydrogen and a second, electronegative atom--whether structurally the two are part of the same molecule or are of different molecules. If bonding occurs between different molecules, it is intermolecular. If it occurs within one molecule, it is intramolecular. The length of a chemical bond indicates its strength. The stronger it is, the shorter it is. Hydrogen bonds are shorter than van der Waals bonds, but longer than covalent and ionic bonds.
Intermolecular Hydrogen Bonding
The outstanding example of hydrogen bonding is water. One hydrogen atom of one water molecule forms a weak bond with one oxygen atom of another water molecule. The other hydrogen atom of the first water molecule can form a bond with the oxygen of a third water molecule. Interestingly, under the special conditions of freezing and pressurization, all hydrogen to oxygen bonds in water can be made to approach equality. This is called symmetric hydrogen bonds, in which each bond possesses a measure of covalent character.
Intramolecular Hydrogen Bonding
An example of an intramolecularly bonded species is 2-cyanoethanol, HO-CH2CH2-CN. In this instance, the hydroxyl hydrogen (the H of the HO- group) is electrostatically drawn to the nitrogen of the cyano group (the N of the -CN group). The resultant structure is a loosely flexible six-member ring--a hexagon--with the skeleton H-O-C-C-C-N. The other hydrogen atoms are attached to the two, central, carbon atoms. Intramolecular bonding can position atoms to favor certain reactions over others.
General Effects of Hydrogen Bonding
Since intermolecular hydrogen bonding draws molecules closer together, liquids experience an increase in density. It requires energy to disrupt these bonds, so hydrogen-bonded liquids experience a higher boiling point. Molecular shapes in the liquid state are affected as is the crystal lattice of solids, because hydrogen bonds, although flexible, distort molecules into specific positions. Water-solubility is increased for hydrogen-bonded compounds, since water can establish hydrogen bonds with dissolved solute.
Polymer and Macromolecule Effects of Hydrogen Bonding
In biologically active macromolecules, hydrogen bonding contributes to higher levels of structure, including protein folding. Hydrogen bonding is largely responsible for the double helix of DNA. Parallel hydrogen bonding (hydrogen bonding between two linear structures) add strength to fibers such as cellulose.
IUPAC: Provisional Recommendations - Definition of the Hydrogen Bond
WW Norton & Company: Hydrogen Bonding in Water
NRC Research Press: Intramolecular Hydrogen Bonds in 2-Cyanoethanol and in Some Nitroalcohols
Published by Vincent Summers
My secular expertise includes 23 years of experience at the National Radio Astronomy Observatory, with a share in NASA's extended Voyager 2 effort. I formerly wrote for Demand Studios, Bukisa, Suite 101, Exa... View profile
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11 Comments
Post a CommentInteresting material - learned something :)
Most people in sciences will tell you, however, that we care little to none about "inter" or "intra" for hydrogen bonding. Such details receive a modicum of interest when you have larger things to worry about :-)
I find your articles fascinating!!! Keep up the good work you are educating us all!!
Thanks for sharing :) Bonding is important to all these molecules and to humans, as well.
You are a wonderful teacher!
Great explanation of the hydrogen bond!
Now you know you are 'way above my head' on this, but thanks for a good article!
Science is not my forte, but I'm glad to learn that something's holding it all together!
Good work. I think I understood two sentences.
Believe it or not, I understood and have heard of this. I feel smart! :))