Organic chemistry as representation

Abstract

Electron redistribution is the cornerstone of our understanding of chemical reactivity. For the vast majority of organic reactions electrons are assumed to move in pairs providing explanatory mechanisms through the generation of intermediate structures. But for many transformations these discrete steps are idealized constructs, involving intermediates assumed but not empirically justified. This unitary perspective predicated on the curved arrow formalism has resulted in the scenario where for many organic transformations our supposed understanding far surpasses our growing knowledge. Reformulating organic mechanisms to include single electron transfer (SET) as a component of, or an alternative to, the prevailing iconic descriptions can provide for a more empirically adequate mechanistic description. In addition using the language of SET presents an opportunity to unify mechanistic concepts under a common donor/acceptor framework.

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Notes

  1. 1.

    The Beilstein database of Organic reactions has logged yearly growth of ca. 250,000 structures, 200,000 reactions and about 40,000 citations from 1979, and as of 2004 contained 9,293,250 chemical reactions (Fialkowski et al. 2005).

  2. 2.

    It was Ingold’s original intent that the electronic effects used to establish the link between structure and energy be separate from those used to connect structure and reactivity. By the time of his 1934 review (Ingold 1934) the through bond inductive effect and the conjugative mesomeric effect had been classified as permanent, what are termed today as polarization effects. However during the course of a reaction time-independent polarization is replaced by time-dependent polarizability, or what Ingold at the time called the inductomeric and electromeric effects. Today the latter terms are no longer used, and mesomerism has been widely replaced by resonance, where \(\chi_{i}\) is a canonical resonance form, \(\chi_{i} = \prod\nolimits_{j} {n_{j} } \varphi_{j}\), of the wave function, \(\Psi = \sum\nolimits_{i}^{{}} {} c_{i} \chi_{i}\) (Healy 2011).

  3. 3.

    The succeeding 20 pages presented what H.C. Brown characterized as “an elaborate system of notation” designed to unify a slew of reactions of bases/nucleophiles/reductants with acids/electrophiles/oxidants under a single donor–acceptor framework. The result, as feared by Mulliken himself, was “excessively” elaborate and never widely adopted.

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Acknowledgements

The author wishes to acknowledge the Welch Foundation (Grant # BH-0018) for its continuing support of the Chemistry Department at St. Edward’s University.

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Correspondence to Eamonn F. Healy.

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Healy, E.F. Organic chemistry as representation. Found Chem (2020). https://doi.org/10.1007/s10698-020-09379-z

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Keywords

  • Organic chemistry
  • Mechanism
  • Representation as reality
  • Electronegativity
  • Resonance