Reaction Mechanism Arrow Drawer

How it works

A curved arrow is a map of one electron pair. The tail sits on the pair that moves, a lone pair or a bond, and the head points to where the pair ends up, a new bond or an atom. Read a mechanism by following the arrows in order: the first arrow makes a bond, the second breaks one, and the charges change to match.

In an SN2 reaction, the nucleophile's lone pair forms a bond to carbon while the carbon-halogen bond breaks, and the halogen leaves with the pair. The carbon is attacked from the back, so the stereochemistry inverts. In a carbonyl addition, the nucleophile attacks the carbon while the pi bond moves onto oxygen. In an E2 elimination, a base takes a proton, the carbon-hydrogen bond becomes the second bond of a double bond, and the leaving group departs, all in one step. In an acid–base proton transfer, the base takes the proton: one arrow runs from the base lone pair to the proton, and a second arrow runs from the O–H bond back onto the oxygen, which keeps the electron pair. The acid becomes its conjugate base and the base becomes its conjugate acid.