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How to calculate the number of active Hydrogen bonds per molecule

Learning Objective: To calculate the number of active hydrogen bonds per molecule and techniques for detecting hydrogen bonds. 

Skill Level – Intermediate

 

Prerequisites: 

 

Chapter: Intermolecular Forces

Sub-topic: Hydrogen Bonding

 

Author's Note: Plato once said, "Everything that deceives may be said to enchant." In the context of hydrogen bonding, the deception is to be enchanted by the thought that the number of hydrogen bonds is equal to the available number of hydrogen bond donors or acceptors. That's not always true. In some cases, the number of hydrogen bonds formed is lower than expected. This section covers the rule that determines its number and illustrates using examples of how many hydrogen bonds form in actual for molecules like NH3, HF, and H2O. We also briefly look at analytical techniques that detect hydrogen bonds in different molecules.

How to calculate the number of active Hydrogen bonds per molecule

The number of Hydrogen bonds depend on type of solvent, solvent concentration, medium (solid, liquid or gas), temperature, pressure, and H-bond strength with few Hydrogen bonds having a mean lifetime of only 10-12 sec (NH3----H2O bond). 

But mainly, the number of Hydrogen bonds the electronegative atom (N, O, or F) in a molecule can form depends on -

1) The number of Hydrogens directly attached to electronegative atom to act as a Hydrogen bond donor. 

2) The number of electron lone pair at....

 

The number of H-bonds an atom can form decreases if there is less...

 

For example, Nitrogen in NH3 has one lone pair and the molecule has three hydrogens. So, ideally one lone pair acting as H-bond acceptor and three Hydrogens as H-bond donors, the molecule should be able to form four Hydrogen bonds. But it only forms two;...

 

 

In Hydrogen Fluoride (HF), the Fluorine has three lone pairs, and the molecule HF ...

Therefore, all the lone pair or all the hydrogens are not always used for intermolecular H-bonding, except in ...

Detection of Hydrogen bonding includes measurement of dipole moments, ....

Subscribe to learn how to calculate the number of active hydrogen bonds per molecule and also ways one can detect hydrogen bonds.

 

Intermolecular Forces
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Bonding In Atoms

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Common Types of Reactions

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Drawing Organic Structures

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Functional Groups in Organic Chemistry

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Fundamentals of Organic Reactions

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Reactive Intermediates

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Stereoisomerism - Conformation and Configurational Isomerism

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