布莱特规则：除非环够大，否则桥环化合物中的桥头原子不可连有双键。如：布莱特规则预测如下两个降冰片烯的异构体是不稳定的。事实也是如此。

布莱特规则之所以存在，主要是因为在小环和中环（小于八元）中，桥头的双键有环张力，特别是角张力。规则可用于预测消除反应的产物。亦可应用于碳正离子以及自由基（不过不如前者常见）机理，因这些中间体倾向于采取键角120°、sp2杂化的平面构型。

违反这一规则的分子称为“反-布莱特化合物”，如2-奎宁环酮四氟硼酸盐。

Bredt's rule is an empirical observation in organic chemistry that states that a double bond cannot be placed at the bridgehead of a bridged ring system, unless the rings are large enough. The rule is named after Julius Bredt.

For example, two of the following isomers of norbornene violate Bredt's rule, which makes them too unstable to prepare: