Illustrated Glossary of Organic Chemistry

Butyllithium: An organolithium reagent bearing a bond between lithium and a carbon of any butane isomer. Uses include a strong base, a nucleophile, or for halogen-metal exchange.
n-Butyllithium
(n-BuLi)		   
sec-Butyllithium
(sec-BuLi or s-BuLi)		   
tert-butyllithium
(tert-BuLi or t-BuLi)