Hydrogen Bonding

Hydrogen bonding is an electrostatic dipole to dipole interaction between molecules, whereas it also has some features of covalent bonding. Hydrogen bonding is directional and strong, produces shorter interatomic distances, and usually involves a limited number of interaction partners. Its strength ranges from 4 kJ to 50 kJ per mole of hydrogen bonds. A bonding that is partially intermolecular is the interaction between a lone pair of an electron-rich donor atom, particularly second-row elements that are Nitrogen, Oxygen, Fluorine, and the antibonding molecular orbital of a bond between hydrogen and a more electronegative atom or group is in hydrogen bonding. 

Generally, such an interacting system is denoted as Dn-H..Ac. where the solid lines denote a polar covalent bond and the dash or the dotted lines indicate the hydrogen bond. IUPAC recommends especially these three centered dots. While hydrogen bonds have both electrostatic and covalent contribution, the degree to which they contribute is currently debatable. The present evidence implies that the contribution which is primary is covalent. 


History

The concept of hydrogen bonding was given in 1912 by T.S. Moore and T.F. Winmill. They used the hydrogen bond to account for the fact that trimethylammonium hydroxide is a weaker base than tetramethylammonium hydroxide. 

Once the hydrogen bonding concept was challenging. In the rosebush city work and the paperwork by a fellow scientist at their laboratories, Maurice Loyal Huggins says Mr. Huggins of this laboratory in some work as yet unpublished has used the idea of the hydrogen kernel which was held between two atoms as the theory regarding certain organic compounds.  


What is Hydrogen Bonding?

When a special type of dipole-dipole attraction to a strongly electronegative atom exists in the vicinity of another electronegative atom with a lone pair of electrons, it forms hydrogen bonding. Hydrogen bonds are generally stronger than ordinary dipole-dipole and dispersion forces, but weaker than true covalent and ionic bonds.

Hydrogen atoms bonds are known as the weak hydrogen bonds to elements such as chlorine and sulphur can serve as a doner, particularly when the carbon or one of its neighbours is electronegative. It was recognized that there are many examples of hydrogen bonding involving  N, O, F, and AC with electronegativity approaching hydrogen. These non-traditional hydrogen bonding interactions are weak bonds. These are increasingly recognized as important control elements in the receptor-ligand interaction in the science of material. It is said to be an interaction which is between an atom from a molecule or it’s a fragment of the molecule which is denoted as  X-H in which X is a lot more electronegative than H, and a group or an atom in the different or same molecule in which there is evidence of bond development.

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Types of Hydrogen Bonding

Hydrogen bondings are of two types, and it is classified as the following:

  • The Intramolecular Hydrogen Bonding

  • The Intermolecular Hydrogen Bonding

Intramolecular Hydrogen Bonding

When a hydrogen bonding is present within a molecule itself, then it is called intramolecular hydrogen bonding.

Intramolecular hydrogen bonding takes place in the two such groups of compounds where one group has a hydrogen atom linked to an electronegative atom and the other contains a highly electronegative atom which is linked to a lesser electronegative atom of the other group.

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Intermolecular Hydrogen Bonding

When there is hydrogen bonding between different types of molecules of the different or the same compounds, then it is called intermolecular hydrogen bonding. Taking an example – hydrogen bonding in water, alcohol, etc.

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Properties of Hydrogen Bonding

The properties of molecular hydrogen, H2 include very low boiling and melting points which result from weak forces of attraction between the molecules. Weak forces of intermolecular attraction are also recognized by the fact that, when hydrogen gas expands from high to low pressure at room temperature, its temperature rises, and the temperature of most other gases falls in the same experiment. The thermodynamic principles, it implies that repulsive forces increase and between hydrogen bond attractive forces between hydrogen molecules at room temperature otherwise the expansion will cool the hydrogen. A key to designing the drugs is hydrogen bonding. According to Lipinski's rule of 5 majority and 10 hydrogen bonds. The interaction exists between the hydrogen-nitrogen and oxygen-hydrogen centers. As with the many other rules such as, the thumb rule, many exceptions also exist.


Bond Strength

The hydrogen bond can vary in strength from weak to strong, the typical enthalpies in vapor include:

F-H...: F(161.5 KJ/Mol or 38.6Kcal/mol)

The strength of intermolecular bonds of hydrogen is most often evaluated by measurements of equilibria between molecules containing donor or acceptor units most often in the solution. The intermolecular strength of bonds can be studied with equilibria between conformers and with and without hydrogen bonds. The method of most important identification of hydrogen bonds also in complicated molecules is known as crystallography, NMR spectroscopy, sometimes. In a particular distance, acceptor and donor which are smaller than the sum of the Van der Waals radii can be taken as the strength of the hydrogen bond.

FAQ (Frequently Asked Questions)

Q1. What are the factors that affect the Hydrogen Bond?

Ans: The extensive property: a molecule that can form more than one hydrogen bond with the neighbouring molecules will have a more extensive hydrogen bond hence, more energy is required to break the hydrogen bond per molecule, and the melting and boiling point is higher.

Q2. What makes the Hydrogen Bond strongest?

Ans: The hydrogen energy bonds are usually attributed to electrostatic interaction. The strongest OHO bonds are in the ionic systems, since electrostatic attraction between a dipole and a monopole is generally greater than between the two poles.

Q3. How is the Hydrogen Bond broken?

Ans: Many mammals cool themselves by sweating. Sweat on evaporation produces a cooling effect, as a large amount of heat is needed to break the hydrogen bonds between water molecules. Temperature reduction extremes near large bodies of water like the ocean.

Q4. Does HCI have no Hydrogen Bonding?

Ans: The atom of chlorine is too long. Despite the electronegativity, the size of the atom is such that its electron density is very low to form hydrogen bonds. This is why we can see that HCI does not display hydrogen bonding while HF does.