Hydrogen Bond

∞ generated and posted on 2022.01.28 ∞

Attraction between stable partial charges as associated with polar substances.

Hydrogen Bonds are weak chemical interactions between portions of substances that possess small excesses of electrons and portions of substances that possess small dearths of electrons.

That is, partial positive charges are attracted to partial negative charges versus attraction between full charges as seen with ionic bonds or with salt bridges. Hydrogen bonds particularly are found between hydrogen atoms carrying stable partial positive charges and other atoms such as oxygen carrying stable partial negative charges. Note that "stable" is rather than "transient", with the latter seen instead with van der Waals interactions.

Partial positive charges are associated particularly with hydrogen atoms that are covalently bound to more electronegative atoms, again such as oxygen but also nitrogen. Similarly, partial negative charges are associated with oxygen, as noted, but also with nitrogen atoms.

Hydrogen bonds not only can be found between molecules (intermolecular) but also within molecules (intramolecular). Between molecules includes the base pairing seen between the two strands making up a double helix of DNA. Within molecules is seen particularly within polypeptides making up proteins but also in terms of the complex RNA secondary structure such as seen with tRNA and rRNA.

Hydrogen bonds and hydrogen bonding are responsible for the remarkable properties of water including that water is a liquid rather than a gas at room temperature, that polar substances so readily dissolve in water, for capillary action, for hydrophobic exclusion, etc.

Here the hydrogen bond forms between hydrogen atoms and oxygen atoms, i.e.,

H – O – H ⋯ O – H,

where the midline horizontal ellipsis is indicative of the hydrogen bond and the en dashes are indicative of polar covalent bonds.