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Hydrogen bond

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Definition

noun

plural: hydrogen bonds

A type of chemical bond that is formed when the slightly positive hydrogen atom of a polar covalent bond forms an electrostatic link with the more electreonegative atom of a polar covalent bond in the same or another molecule


Details

Overview

A chemical bond holds atoms, ions, or molecules together in a chemical compound. Three types of chemical bonds that are deemed as biologically important are (1) ionic bonds, (2) covalent bonds, and (3) hydrogen bonds.


Hydrogen bond - characteristics

A common chemical bond. Hydrogen bond is a common type of chemical bond in organisms. As the name suggests, this type of bond involves a hydrogen atom. The hydrogen is attracted to a strongly electronegative atom, such as oxygen, fluorine, or nitrogen of a polar covalent bond in the same or another molecule. The link between the hydrogen atom and an electronegative atom is a strong dipole-dipole attraction. A hydrogen bond can occur in organic molecules (e.g. DNA and proteins) and inorganic molecules (e.g. water molecules). Liquids such as water with hydrogen bonds are called associated liquids.


Electrostatic dipole-dipole interaction. Ions or atoms of opposite charges tend to be attracted towards each other. This is as opposed to the phenomenon wherein ions or atoms with the same charge tend to repel. In this case, this is called electrostatic repulsion. A hydrogen bond is a partially electrostatic attraction that works between a hydrogen atom (i.e. bound to a more electronegative atom or group of atoms) and an adjacent atom with a lone pair of electrons. This adjacent atom with lone pair of electrons serves as the hydrogen bond acceptor whereas the hydrogen attached to a more electronegative atom serves as the hydrogen bond donor. The proton acceptor is the electronegative atom that is not covalently bound to the hydrogen. The proton donor is the atom covalently bound to the hydrogen. The proton donor is a Lewis base.


Weak bond. A hydrogen bond is a weak type of chemical bond compared with covalent and ionic bonds. It has only about 1/20 the strength of a covalent bond.[1] It is also weaker than the ionic bond. Nevertheless, it is somewhat stronger than a van der Waals interaction. Depending on the atoms involved, the geometry, and the environment, the energy may vary from 1 to 40 kcal/mol.[2]


H···Y system. The hydrogen bond is represented by dots between the hydrogen (H+) and the strongly electronegative atom.


Intermolecular vs. Intramolecular hydrogen bonds

A hydgrogen bond may be intermolecular or intramolecular. An intermolecular hydrogen bond occurs between separate molecules. An intermolecular hydrogen bond is one that which occurs within the same molecule. An example of an intermolecular hydrogen bond formation is that occurring in water molecules. A water molecule (H2O) may form transient hydrogen bond with an adjacent water molecule. Since a water molecule is polarized, the electronegative hydrogen of one water molecule is electrostatically attracted to the electropositive oxygen atom of the nearby water molecule. Hydrogen bond formation in water accounts for the latter's distinctive properties such as high boiling point (100 °C), high surface tension, specific heat, and heat of vaporization.[1]

An intramolecular hydrogen bond is exemplified by that in proteins and nucleic acids. DNA, for instance, has a double helical structure that is largely due to the hydrogen bonds between paired nitrogenous bases.

Intermolecular and intramolecular hydrogen bonds may occur at the same time in a biological structure. For instance, a strand of cellulose may have hydrogen bonds within and between cellulose molecules.


Hydrogen bond vs. Covalent bond

One of the major distinctions between a covalent bond and a hydrogen bond is the electronegativity of the atoms involved. In a covalent bond, the electronegativities of the two atoms are comparable. Conversely, hydrogen bond forms when the slightly positive hydrogen atom of a polar covalent bond forms an electrostatic link with the more electronegative atom of a polar covalent bond in the same or another molecule.


Similar to a covalent bond, the hydrogen bond is a common chemical bond in organic compounds, particularly nucleic acids and proteins. The hydrogen bond is responsible for the formation of the secondary and the tertiary structures of nucleic acids and proteins.


Hydrogen bond vs. Ionic bond

Hydrogen bond forms when the slightly positive hydrogen atom of a polar covalent bond forms an electrostatic link with the more electronegative atom of a polar covalent bond in the same or another molecule. The hydrogen bond, though, is a weaker chemical bond than ionic bonds at most.


Importance

Hydrogen bond is essential to organisms as it is responsible for the formation of important molecules. It occurs in inorganic molecules (e.g. water) and organic molecules (e.g. DNA and proteins). Hydrogen bonds are responsible for the secondary and tertiary structures of important biomolecules such as nucleic acids and proteins.

Hydrogen bond has a structural role during the formation of polymers, both synthetic (e.g. nylon) and natural (e.g. cellulose). Hydrogen bonds account for the crystallization and the reinforcement of materials. In aramid fiber, the hydrogen bonds help in stabilizing the linear chains laterally.


Trivia

The term hydrogen bond was first mentioned in 1912 by T.S. Moore and T.F. Winmill. [3]


Supplementary

Etymology

  • French hydrogène, from Ancient Greek ὕδωρ (húdōr, meaning “water”) + γεννάω (gennáō, meaning “I bring forth”)
  • Old English beand, bænd, bend (“bond", "chain”)


Further reading

See also


Reference

  1. Rae-Dupree, J. & DuPree, P. (2019, January 1). 4 Types of Chemical Bonds - dummies. Retrieved from https://www.dummies.com/education/science/anatomy/4-types-of-chemical-bonds/
  2. Steiner, T. (2002). "The Hydrogen Bond in the Solid State". Angew. Chem. Int. Ed. 41: 48–76. doi:10.1002/1521-3773(20020104)41:1<48::AID-ANIE48>3.0.CO;2-U
  3. Moore, T. S. & Winmill, T. F. (1912). "The state of amines in aqueous solution". J. Chem. Soc. 101: 1635. doi:10.1039/CT9120101635



Notes


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