Why does an SN2 reaction invert the stereocenter?
3D model · turn it, step through it, tap the parts
An interactive 3D scene of an SN2 reaction: hydroxide approaches the carbon from the side opposite bromine, its lone pair filling the C–Br antibonding lobe; at the five-coordinate transition state the three groups flatten, and as C–O forms and C–Br breaks they flip through like an umbrella, turning the S reactant into the R product.