Alpha effect

<p>The alpha effect refers to the increased <a href="/facts/Nucleophile/xYccoaJQ">nucleophilicity</a> of an <a href="/facts/Atom/FoQ4kGN5">atom</a> due to the presence of an adjacent (alpha) <a href="/facts/Atom/FoQ4kGN5">atom</a> with <a href="/facts/Lone_pair/Q6kEAC4g">lone pair</a> <a href="/facts/Electron/L0KBo5cW">electrons</a>. This first atom does not necessarily exhibit increased <a href="/facts/Basicity/M9wA7qeM">basicity</a> compared with a similar atom without an adjacent electron-donating atom, resulting in a deviation from the classical Brønsted-type reactivity-basicity relationship. In other words, the alpha effect refers to nucleophiles presenting higher nucleophilicity than the predicted value obtained from the Brønsted basicity. The representative examples would be high nucleophilicities of <a href="/facts/Hydroperoxide/w7hdgtVF">hydroperoxide</a> (HO2−) and <a href="/facts/Hydrazine/G7P5ITzU">hydrazine</a> (N2H4). The effect is now well established with numerous examples and became an important concept in mechanistic chemistry and biochemistry. However, the origin of the effect is still controversial without a clear winner.
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Alpha effect open-in-new

Alpha effect