Lewis base?

Atomic or molecular chemical species having a highly localized HOMO (The Highest Occupied Molecular Orbital) act as Lewis bases. These chemical species have the ability to donate an electron pair to a given Lewis acid in order to form an adduct, as discussed earlier.

Examples of Lewis bases which have an ability to donate an electron pair are listed below.

• Pyridine and the derivatives of pyridine have the ability to act as electron pair donors. Thus, these compounds can be classified as Lewis bases.
• The compounds in which Oxygen, Sulphur, Selenium, and Tellurium (which belong to group 16 of the Periodic Table) exhibit an oxidation state of -2 are generally Lewis bases. Examples of such compounds include water and ketones.
• The simple anions which have an electron pair can also act as Lewis bases by donating these electrons. Examples of such anions include H^– and F^–. Even some complex anions, such as the sulfate anion (SO₄^2-) can donate pairs of electrons.