In this post we will see how it is possible for a molecule to form Hydrogen bonding even if it doesn’t have H directly bonded to an electronegative element. In order to find the reason behind it, we have to review Hydrogen bonding.
Hydrogen bond is formed between partially negative element and partially positive Hydrogen, in which, electronegative element of one molecule gives its lone pair of electrons to electron deficient Hydrogen of other molecule. That means, in this process one molecule acts as a donor and other behaves as an acceptor.
Same molecule can act both as a donor and an acceptor. Generally hydrogen bond donors are the molecules in which H is directly attached to electronegative element like H2O, NH3, HF, CH3OH etc. and Hydrogen bond acceptors are the molecules that do not have H directly bonded to electronegative element like diethyl ether CH3OCH3.
Let’s take an example to understand it. If a molecule of H2O comes closer to NH3 molecule. There are two possibilities of Hydrogen bonding; either O of water donates its lone pair to the H of NH3 or N of NH3donates its lone pair to the H of water molecule. In the first case water accepts H from NH3 and NH3 acts as donor, while in the latter case they reverse the role of donor and acceptor. Which one will behave as a donor and an accepter depends solely on chance.
If a molecule of CH3OCH3 comes closer to the H2O molecule, CH3OCH3 acts as Hydrogen bond accepter and H2O acts as donor. Thus CH3OCH3 molecules make Hydrogen bonds with water molecules.
The quality of water to make Hydrogen bond with other molecules makes it universal solvent. Molecules which make Hydrogen bond with water are soluble in water.
In some conditions Hydrogen bond is formed inside the same molecule and it is called Intramolecular hydrogen bond. In the next post we will study the examples of Intramolecular hydrogen bonding.
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