C₈H₂₀Pb, an organometallic compound used as a gasoline additive that prevents engine knocking. Leaded fuel allows for better efficiency and decreased knocking in internal combustion engines, but the lead released in car emissions, as lead oxides, is very toxic to humans. Lead would get deposited on the road and get mixed into urban dust. Teraethyl lead incorporation in gasoline was developed by Thomas Midgley, Jr. , later the inventor of chlorofluorcarbons. The advent of the catalytic converter's use in the 1970's precluded the use (in the U. S. ) of leaded gasoline because Pb poisoned the metals used in that device. TEL was therefore substantially phased out over the next 20 years.

1,2,3,4-tetramethylbenzene (C₁₀H₁₄)

1,2,3,5 Tetramethylbenzene.