The reaction of butan-2-ol with concentrated aqueous hbr goes with partial racemization, giving more inversion than retention of configuration. propose a mechanism that accounts for racemization with excess inversion. (b) under the same conditions, an optically active sample of trans-2-bromocyclopentanol reacts with concentrated aqueous hbr to give an optically inactive product, (racemic) trans-1,2- dibromocyclopentane. propose a mechanism to show how this reaction goes with apparently complete retention of configuration, yet with racemization.