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 superimposed over 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. Arrow pushing is also used to describe how positive and negative charges are distributed around organic molecules through resonance. It is important to always remember, however, that arrow pushing is a formalism and electrons (or rather, electron density) do not move around so neatly and discretely in reality.

Recently, 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.

Organic chemists use two types of arrows within molecular structures to describe electron movements. Single electrons' trajectories are designated with single barbed arrows, whereas double-barbed arrows show movement of electron pairs.

When a bond is broken, electrons leave where the bond was and this is represented by a curved arrow pointing away from the bond and ending the arrow pointing towards the next unoccupied molecular orbital . Similarly, organic chemists represent the formation of a bond by a curved arrow pointing between two species.

For clarity, when pushing arrows, it is best to draw the arrows starting from a lone pair of electrons or filled bonds (sigma, pi) and ending in an unfilled molecular orbital, allowing the reader to know exactly which electrons are moving and where they are ending.

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