Arrow pushing

Arrow pushing or electron pushing is a technique used to describe the progression of organic chemistryreaction mechanisms. It was first developed by Sir Robert Robinson. In using arrow pushing, "curved arrows" or "curly arrows" are drawn on the structural formulae of reactants in a chemical equation to show the reaction mechanism. The arrows illustrate the movement of electrons as bonds between atoms are broken and formed, allowing for a pictorial understanding of the source of electrons in a reaction (nucleophiles), sites to which they are attracted (electrophiles), and atoms or groups where they eventually end up (leaving groups), giving a picture of the overall direction of their movement. Arrow pushing never directly show the movement of atoms; it is used to show the movement of electron density, which indirectly shows the movement of atoms themselves.

Arrow pushing is also used to describe how formal positive and negative charges are redistributed around organic molecules through resonance. It is important to remember, however, that in contrast to the usual goal of showing electron flow in a reaction, the use of arrow pushing to aid in drawing alternative resonance forms of a molecule is purely a formalism for bookkeeping of formal charges and electrons, and no movement of electrons (or rather, electron density) takes place in that case: it is merely a tool to understand how electrons are distributed in a delocalized system.

Arrow pushing has been extended to inorganic chemistry, especially to the chemistry of s- and p-block elements. It has been shown to work well for hypervalent compounds.