Shown below is an example of regioselectivity and stereospecificity of the oxymercuration reaction with substituted cyclohexenes. A bulky group like "t"-butyl locks the ring in a chair conformation and prevents ring flips. With 4-"t"-butylcyclohexene, oxymercuration yields two products – where addition across the double bond is always "anti" – with slight preference towards acetoxymercury group "trans" to the "t"-butyl group, resulting in slightly more "cis" product. With 1-methyl-4-"t"-butylcyclohexene, oxymercuration yields only one product – still "anti" addition across the double bond – where water only attacks the more substituted carbon. The reason for "anti" addition across the double bond is to maximize orbital overlap of the lone pair of water and the empty orbital of the mercuronium ion on the opposite side of the acetoxymercury group. Regioselectivity is observed to favor water attacking the more substituted carbon, but water does not add "syn" across the double bond which implies that the transition state favors water attacking from the opposite side of the acetomercury group.