Arrow pushing
Technique using curved arrows to show electron movement in reactions.
Arrow pushing, also known as electron pushing, is a technique used to describe the progression of organic chemistry reaction mechanisms. The method uses curved arrows drawn on structural formulae to show the movement of electrons as bonds are broken and formed, providing a pictorial understanding of nucleophiles, electrophiles, and leaving groups.
- field
- Organic chemistry, inorganic chemistry
- known_for
- Development of arrow pushing (electron pushing) notation
- first_developed_by
- Sir Robert Robinson
Lore & Background
Organic chemists use two types of arrows: single-barbed arrows for single electron movement and double-barbed arrows for electron pairs. The arrow's tail is drawn at a lone pair or bond (electron source), and its head points toward an electron sink. Arrow pushing never directly shows atom movement; it shows electron density movement, which indirectly indicates atom movement. The technique is also used to describe redistribution of formal charges through resonance, though this is purely a formalism for bookkeeping—no actual electron movement occurs in resonance. Arrow pushing has been extended to inorganic chemistry, particularly for s- and p-block elements, and works well for hypervalent compounds. Arrow pushing illustrates bond breaking via homolytic cleavage (two single-barbed arrows, producing free radicals) or heterolytic cleavage (one double-barbed arrow, producing ions). It is applied to acid-base reactions, SN1 and SN2 reactions, and E1 eliminations, showing electron flow from nucleophiles to electrophiles or leaving groups.
Reader's Guide
Arrow pushing is a foundational tool in organic chemistry, enabling chemists to visualize electron flow during reactions. This notation clarifies mechanisms such as nucleophilic substitution, elimination, and acid-base reactions. It also aids in drawing resonance structures, though this use is a formal bookkeeping method rather than depicting actual electron movement. The technique has been extended to inorganic chemistry, including hypervalent compounds. By distinguishing homolytic (radical) and heterolytic (ionic) bond cleavage, arrow pushing provides a systematic way to understand reaction pathways and predict products. Its clarity and consistency make it indispensable for teaching and research in chemistry.
Did You Know?
- Single-barbed arrows denote movement of single electrons; double-barbed arrows denote movement of electron pairs.
- Arrow pushing never directly shows the movement of atoms; it shows movement of electron density.
- The use of arrow pushing for resonance forms is purely a formalism for bookkeeping, with no actual electron movement taking place.
More in Organic Chemistry And Reaction Mechanisms 1-22
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