CHEM 223 Nucleophilic Strength

basicity

the equilibrium constant from abstracting a proton

nucleophilicity

rate of attack on the electrophilic carbon atom

• strong nucleophiles are strong bases, but not all strong bases are nucleophilic

ROH

weak nucleophile

H₂O

weak nucleophile

F^-

weak nucleophile

RCOOH

weak nucleophile

Cl^-

moderate nucleophile

RCOO^-

moderate nucleophile

RSH, RSR

moderate nucleophile

NH₃

moderate nucelophile

RNH₂

moderate nucleophile

Br^-

moderate nucleophile

HO^-, RO^-

strong nucleophile

R₃N

strong nucleophile

^-CN

strong nucleophile

RCC^-

strong nucleophile

I^-

strong nucleophile

HS^-,RS^-

strong nucleophile

NH₂^-

strong nucleophile

R₃P

strong nucleophile

negative charge

increases nucleophilicity, increases basicity

increasing size (and polarizability)

increases nucleophilicity, decreases basicity

increasing electronegativity

decreases nucleophility (larger electron clouds easier to distort to attack), decreases basicity (larger volume stabilizes negative charge)

steric hinderance

decreases nucleophilicity, no effect on basicity

protic solvent

supresses nucleophiles (through H bonding)