Bredt's rule

In organic chemistry, Bredt's rule is the empirical observation that bridged molecules tend only to possess a double bond at the bridgehead in large ring systems. The rule is named after Julius Bredt, who first discussed it in 1902 and codified it in 1924.

An anti-Bredt molecule is a moecule which does not follow Bredt's rule. For example, two of the following norbornene isomers violate Bredt's rule and are too unstable to prepare: