Hydrogen Bond and Its Importance
A hydrogen bond exists between electronegative atoms such as oxygen, chlorine or fluorine of molecule having a partial negative charge and a hydrogen atom in contact with an electronegative atom of a different molecule having a partial positive charge. It is an attraction (dipole-dipole) between atoms.
The hydrogen bond is formed as the hydrogen donor is electronegative. So, electron pair is pulled closer to its nucleus and from hydrogen atom creating a partial positive charge on hydrogen atom. This leads to dipole-dipole interaction amongst hydrogen atom at the acceptor site leading to the formation of the hydrogen bond.
Hydrogen bond (H-bonding) has a strength between covalent bonds or ionic bonds and van der Waal’s forces. H-bonding has 5% of the strength of the covalent bond formed between O-H. Even the bond length depicts the same, hydrogen bond length is 1.97 angstroms whereas covalent bond length is 0.96 angstroms.
Hydrogen bonds are of two types:-
Intramolecular hydrogen bond
It occurs within the single molecule. It could be the case when there is the presence of two functional groups within the same molecule forming a hydrogen bond. There must be the presence of hydrogen donor and acceptor and there must be in close proximity to each other in order to form H-bonding. Eg: – ethylene glycol which has 2 hydroxyl groups forms hydrogen bonding due to molecular geometry.
Intermolecular hydrogen bond
It occurs between two molecules. Hydrogen donors and acceptors should be there for interaction. Eg- H-bond between NH3 and H2O molecule.
H-bonding affects the boiling point like water (H2O) has a higher boiling point than HF although it has more molar mass. It occurs due to the presence of more hydrogen bond per molecule. It also has an effect on viscosity as substances with more hydrogen bonds have a higher viscosity than others.
Hydrogen bonds have a great role in biochemistry and they tend to produce characteristic properties of water like boiling point of water is 100ºC, if H-bond will not be there then water will boil at -80ºC leading to loss of water from oceans and lakes and can create problems of survival on earth.
The double helical structure of deoxyribose nucleic acid (DNA) exist due to the presence of hydrogen bonds between base pairs in the middle.
The H-bonding exist with amino acids leads to the formation of proteins, the further secondary structure of proteins the helix and pleated sheet occur because of hydrogen bonding. Even functioning of hemoglobin is due to H-bonding. It consists of four subunits and these subunits are formed of proteins, which gets coiled into helices due to the presence of H-bonds. The shape formed with hydrogen bond helps in functioning of hemoglobin.
H-bonding also helps in the transportation of water in plants. H-bonding between water molecules as well as with cellulose chain present in walls of plant cells leads to capillary action, this helps plants to pull water up from roots. Also due to H-bonding, there is the formation of long-chain water molecules that control the force of gravity and water can reach up to the high altitude of leaves.