Arrow-Pushing Guide

Quick Guide to Arrow-Pushing and Key Reactions

Goals

hi

Types of Arrows in Mechanisms

The Two Types of Arrows used in Mechanisms.

Representation of electron movement: Representation of electron movement: two-electron (1 bond) processes (Full-arrow →) vs. one-electron (half bond) processes (Half-arrow ↷).

In organic and inorganic mechanisms, arrows are used to show electron movement.

Full Arrows (→)

A full curved arrow represents the movement of two electrons, usually in bond formation or breaking. This applies to:

• Nucleophilic attacks
• Resonance structures
• Electrophilic and nucleophilic reactions
  • Nucleophiles attack electrophiles by donating an electron pair to form a new bond.
  • Electrophiles receive the nucleophillic attack to accept an electron pair to form a new bond.

Nucleophiles donate electron pairs (electron-rich) vs. Electrophiles accept electron pairs (electron-poor).

Half Arrows (↷)

A half-arrow represents the movement of one electron, commonly seen in:

• Radical reactions
• Homolytic bond cleavage
• Radical propagation steps

There will be lots of examples in the entries of Reaction Repo of all reactions mentioned

Applications of the Arrows

Bond Formation

Full Arrow

Half Arrow

Forming Resonance Structures

Resonance forms of DMSO.

DMSO is capable of undergoing resonance. The first step (1) towards the Swern Oxidation

DMSO undergoes resonance, which is represented using a full arrow, indicating the movement of two electrons (one bond). This differs from one-electron processes (shown by half-arrows). The electron pair from the S=O double bond shifts toward oxygen, converting it into a single bond. Since oxygen gains an extra lone pair, it takes on a negative formal charge, while sulfur loses electron density, resulting in a positive charge.