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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.
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.
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Use of oxygen or sulfur as the nucleophilic atom causes minor differences in catalysis. Compared to oxygen , sulfur 's extra d orbital makes it larger (by 0.4 Å) [ 29 ] and softer, allows it to form longer bonds (d C-X and d X-H by 1.3-fold), and gives it a lower p K a (by 5 units). [ 30 ]