Breslow Reference Structure

Figure 8. Resonance energies per n electron in units of fi for the conjugated monocyclic hydrocarbons using the Breslow reference structure and the Hiickel computational method.

A -Alkylated thiazolium and benzothiazolium salts also experience base-promoted deprotonation at the 2-position to form ylides. Such compounds, often referred to as TV-heterocyclic carbene (NHC), are nucleophilic catalysts in benzoin condensation. In 1943, Ugai and co-workers reported that thiazolium salts catalyze self-condensation of benzaldehyde to generate benzoin via an umpoulong process. Breslow at Columbia University in 1958 proposed thiazolium ylide as the actual catalyst for this transformation. In this mechanism, the catalytically active species was represented as a thiazolium zwitterion, the resonance structure of an NHC, and the reaction was postulated to ensue via the enaminol or the Breslow intermediate. ... 

The vrater structure is modified by the presence of solutes, with effects referred to as structure-making or breaking, salting-out or salting-in, antichaotropic or chaotropic, pro- or antihydrophobic. " Such effects modify the kinetics and selectivity outcome of hydrophobic effect driven reactions, as shown by Breslow who reported the acceleration of the aqueous Diels-Alder reaction due to the presence of lithium chloride and by Lubineau and Queneau who later proved the entropic origin of this activation by determining the activation parameters. ... 

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