Illustrated Glossary of Organic Chemistry

Acid: (1) A Bronsted acid or a Lewis acid. In common chemistry usage, the term 'acid' usually refers to a Bronsted acid, whereas when a Lewis acid is under discussion the terms 'Lewis acid' or 'electrophile' are used. Acidity refers to the strength of an acid (its ability to donate a proton to another molecule). A weakly acidic molecule does not donate a proton readily, and has a high pKa (example: water; pKa 15.7), whereas a strongly acidic molecule donates a proton readily and has a low pKa (example: sulfuric acid; pKa -10).

Sulfuric acid (H2SO4) is a strong Bronsted acid (pKa -10). When sulfuric acid is under discussion it is called an acid or a Bronsted acid.

Aluminum chloride (AlCl3) is a Lewis acid because the aluminum atom has an open valence shell. When aluminum chloride is under discussion it is called a Lewis acid or an electrophile.

       (2) A slang term for LSD.