Arrow pushing

Arrow pushing or electron pushing is a technique used to describe the progression of organic chemistry reaction 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. It is important to note that 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 positive and negative charges are distributed around organic molecules through resonance. It is important to remember, however, that arrow pushing is a formalism and electrons (or rather, electron density) do not move around so neatly and discretely in reality. 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. The representation of reaction mechanisms using curved arrows to indicate electron flow was developed by Sir Robert Robinson in 1922. Organic chemists use two types of arrows within molecular structures to describe electron movements. Single electron's trajectories are designated with single barbed arrows, whereas double-barbed arrows show movement of electron pairs. The arrow's tail is drawn at either a lone pair of electrons on an atom or a bond between atoms, an electron source or area where there is relatively high electron density. Its head points towards electron sinks, or areas of relatively low electron density. When a bond is broken, electrons leave where the bond was; this is represented by a curved arrow pointing away from the bond and ending with the arrow pointing towards the next unoccupied molecular orbital.