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Nucleophilicity is closely related to basicity. The difference between the two is, that basicity is a thermodynamic property (i.e. relates to an equilibrium state), but nucleophilicity is a kinetic property, which relates to rates of certain chemical reactions. [1]
H is a measure of the basicity of the nucleophile relative to protons, as defined by the equation: = + where the pK a is that of the conjugate acid of the nucleophile and the constant 1.74 is the correction for the pK a of H 3 O +. E n is the term Edwards introduced to account for the polarizability of the nucleophile
This first atom does not necessarily exhibit increased basicity 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 ...
In a polar aprotic solvent, nucleophilicity increases up a column of the periodic table as there is no hydrogen bonding between the solvent and nucleophile; in this case nucleophilicity mirrors basicity. I − would therefore be a weaker nucleophile than Br − because it is a weaker base.
As the name suggests, a non-nucleophilic base is a sterically hindered organic base that is a poor nucleophile.Normal bases are also nucleophiles, but often chemists seek the proton-removing ability of a base without any other functions.
The basicity and nucleophilicity of carbanions are determined by the substituents on carbon. These include the inductive effect. Electronegative atoms adjacent to the charge will stabilize the charge; the extent of conjugation of the anion. Resonance effects can stabilize the anion.
Similarly, nucleophilicity is defined as the affinity of an electron-rich species, known as a nucleophile, to donate electrons to another species. [30] Trends in the periodic table are useful for predicting an element's nucleophilicity and electrophilicity.
This difference arises from acid/base reactions between protic solvents (not aprotic solvents) and strong nucleophiles. While it is true that steric effects also affect the relative reaction rates, [ 12 ] however, for demonstration of principle for solvent polarity on S N 2 reaction rates, steric effects may be neglected.