reactivity of carbon centered nucleophile with electrophile

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If this above explanation is confusing to you, you may also compare how good the leaving groups are. The sharing of electrons will be less favorable in the resonance form of compound III than the resonance form of compound I.įor compound IV, both resonance structures are equally stable, and the molecule will exist as an average of both structures, placing a fair amount of electron density at the carbonyl carbon, drastically reducing the electrophilicity of the central carbon. We may conclude that the resonance form of compound III contributes less to the true existence of the molecule, as oxygen is more electronegative. Now compare compounds I and III. Resonance for these molecules is essentially identical, with a nitrogen atom in compound I and an oxygen atom in compound III. This is not the case in any other pictured substrate. The resonance forms below each contribute very little to the overall molecule. Note: Remember, resonance diagrams show possible electron distributions, and a molecule exists as a weighted average of these possibilities, favoring the more stable ones.Ĭompound II is the most electrophilic substrate, as the lone pair on the central oxygen molecule must be shared between two carbonyls. This molecule will be least stable and most reactive.

To determine which is the most electrophilic, we must identify the resonance diagram below that contributes the least to the overall molecule. Resonance diagrams for all four substrates show how electrons contained in the leaving group's heteroatom may be shared throughout the carbonyl system, effectively placing a partial negative charge on the electrophilic carbon. As the first step in a substitution reaction involves a nucleophilic attack at an electrophilic carbonyl carbon, we must consider the varying reactivity of the electrophilic carbonyl center. Resonance diagrams, as well as an understanding of electronegativity, will help us understand the degree to which this effect is observed in a substrate.

Reactivity of carbon centered nucleophile with electrophile