A Consistent System of Curved Electron Arrows

TCE

The Chemical Educator

ISSN: 1430-4171 (electronic version)

Table of Contents

Abstract Volume 3 Issue 5 (1998), S1430-4171(98)05251-8

A Consistent System of Curved Electron Arrows

Timothy S. Eckert

Department of Chemistry, Carthage College, Kenosha WI 53140

Published online: 1 October 1998

Abstract. Students of organic chemistry find it difficult to properly use electron arrows. Traditional arrows do not end at one type of location. Whereas the vast majority end at an atom, an arrow that indicates formation of a p bond points to a bond instead. Rethinking electron arrows leads to the following four rules, which form a consistent system: (1) An electron arrow always begins at an electron pair, either bonding or nonbonding. One arrow begins at the nucleophilic electron pair, if any. (2) An electron pair always remains attached to an atom, normally indicated by its arrow. (3) An electron arrow always ends at an atom, not at a bond. One arrow ends at the electrophilic atom, if any. (4) In a series of arrows for one mechanistic step, a succeeding arrow begins by the atom where the preceding arrow ends. This system of electron arrows is superior because the rules can be more generally applied, the arrows reflect the nucleophilicity of electron pairs, the arrows carry more meaning, the arrows in a series flow more directly from one to the next, and the arrows clearly prescribe products.

Key Words: In the Classroom; curved arrows; electron arrows; organic chemistry; mechanisms; symbols

(*) Corresponding author. (E-mail: eckert@carthage.edu)

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