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Chemistry · Glossary

What is Electron-donor and electron-acceptor sites?

Also known as: electron-donor site · electron-acceptor site

Definition 40.1 School Chemistry — Grades 1 to 12 · Chapter 40 — Reaction Mechanisms: Curly Arrows

An electron-donor site of a molecule or an ion is a place rich in electrons, able to give a pair to form a new bond: a lone pair, a double bond, an atom carrying a negative charge or a partial charge δ−\delta^-. An electron-acceptor site is a place poor in electrons, able to receive a pair: an atom carrying a positive charge or a partial charge δ+\delta^+.

Electron-poor carbon atoms (+, acceptor sites) next to electron-rich, electronegative atoms (-, with lone pairs: donor sites).
Electron-poor carbon atoms (δ+\delta^+, acceptor sites) next to electron-rich, electronegative atoms (δ−\delta^-, with lone pairs: donor sites).

Examples

Example 40.2 (Sites in two molecules)

In bromoethane, CHX3−CHX2−Br\ce{CH3-CH2-Br}, bromine is more electronegative than carbon: the carbon bonded to it carries δ+\delta^+ (acceptor site), the bromine δ−\delta^- and three lone pairs. In propanone, the oxygen of the C=O\ce{C=O} group carries δ−\delta^- and two lone pairs (donor sites), its carbon δ+\delta^+ (acceptor site). The hydroxide ion OHX−\ce{OH-}, with its negative charge and three lone pairs, is a strong donor.

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