how to distinguish strong/weak Nucleophile and base?

[kies89]

i think - on the O makes strong Nu
and Cl-, Br-, I-,F-, CN-, N3- are strong nu(weak base)
bulky one is strong base (weak Nu)

this is only things i know

for example NaOCH3 is strong Nu but how do you know that?

is there any rule or method distinguish which is strong base or Nu?

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[erikin1986]

nucleophilicity is dependent on size, electronegativity, and polarizability. and to an extent what type of solution it is in.

size: smaller the better because it will be less hindered to "attack"
electronegativity: higher the electronegative the less the molecule will react because it wants to hold onto its electrons
polarizability: this is the ability to distort the electron cloud of a substrate, making the nucleophile easier to "attack"

In polar aprotic solvent, nucleophilicity goes hand in hand with base strength

 

[Davermz450]

Try this chart, I hope it helps a little

http://www.chemistry.sdsu.edu/courses/CHEM232/review/Substitution_vs_Elimination.pdf