Identity of the Nucelophile

Nucleophiles and Bases

Are structurally similar, both have a lone pair of electrons or a $\pi$ bond. They differ in what they attack

Bases

Attack protons

Nucleophiles

Attack carbons

Nucelophilicity

A measure of how readily an atom donates its electron pair to the other atom (usually a partially positive carbon)

• It is characterized by the rate constant, k, making it a kinetic property

Basicity

A measure of how readily an atom donates its electron pair to a proton (partially positive hydrogen).

• It is characterized by the equilibrium constant (Ka or Kb), making it a thermodynamic property

Stronger base

For two nucleophiles with the same nucleophilic atom, the ___________ is the stronger nucleophile

negatively charged

A ________ nucleophile is always a stronger nucleophile than its conjugate acid

polarizability

Basicity does NOT affect nucleophilicity going down a column because of _________.

• As the _________ of an atom increases (down a column), then nucleophilicity increases (in protic solvents only)

Steric hindrance

Cause a decrease in reactivity due to the presences of bulky groups at the reactive site

• _______ decreases nucleophilicity but NOT basicity

Nonnucleophilic bases

Sterically hindered bases that are poor nucleophiles