This Day in Science History - January 19 - Benzene Nomenclature

January 20^th marks the passing of Carl Gräbe. Gräbe was a German organic chemist who discovered a method to synthesize the distinctive red alizarin dye with Carl Liebermann. This discovery greatly reduced the cost of the red dye that was previously only available from the madder plant.

Gräbe was also the chemist who introduced the nomenclature used to describe bond locations on benzene rings. Benzene is a ring of carbon atoms forming a hexagon. When two functional groups attach themselves to different points of the hexagon, different prefixes are used to differentiate different patterns. Gräbe introduced the use of the prefixes para-, meta-, and ortho- to the organic chemist's dictionary. The para- prefix indicates the functional groups are attached on opposite carbon atoms. Meta- is used to indicate when there is a one carbon atom gap between functional groups. Ortho- is used when two functional groups are on adjacent carbon atoms.