Why basicity is a thermodyanamic property and nucleophilicity is a kinetic property?

Answer 1

In chemistry, thermodynamics is concerned with conditions at equlibrium (reversible processes) and kinetics is concerned with reaction rates, typically of irreversible processes. Acid-base phenomena are completely reversible. They are described by pKa's and pKb's, which are derived from Ka's and Kb's, which are in turn derived from Keq's, which are ultimately derived from delta G's and free energy calculations. These are all thermodynamic properties, the properties of these compounds when equilibrium is reached. Nucleophilicity describes the readiness of a molecule to react with a substrate (an electrophile). "Readiness to react" describes reactivity and reaction rates, kinetic processes. Many nucleophilic attacks (Sn2 reactions for example) have unfavorable and/or insignificant backwards reactions, so they are mostly kinetic processes because they are "irreversible." However, many reactions in organic chemistry are completely reversible, and analysis of equilibria and thermodynamic calculations are meaningful. Examples of this include aldol condensations and many Sn1 reactions, which also involve nucleophiles. The bottom line is you have to look at the whole reaction - if it is reversible, thermodynamics govern, if it is irreversible, kinetics play a larger role in terms of what products you get and the ratio of product(s) to reactant(s).

Answer 2

Basicity relates to the equilibrium position of a reaction where a base accepts a proton, which is a thermodynamic property determined by the stability of the products and reactants. Nucleophilicity, on the other hand, is a kinetic property because it involves the rate at which a nucleophile attacks an electrophile in a chemical reaction, which is more related to reaction kinetics.