good/bad nucleophile?

[IntelInside]

I know good nucleophile is use in SN2 reactions and poor nucleophile is useed in SN1 reactions. The way that I determine if something is a good nucleophile is if it can stabilize its negative charge relatively....is this a correct way of thinking about it. Like size, electronegativity, resonance?

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[phEight]

I know good nucleophile is use in SN2 reactions and poor nucleophile is useed in SN1 reactions. The way that I determine if something is a good nucleophile is if it can stabilize its negative charge relatively....is this a correct way of thinking about it. Like size, electronegativity, resonance?

Basically, it's fair to relate nucleophilicity to basicity, unless steric issues are involved. Stronger the base, stronger the Nu, unless it's bulky. Perhaps others may give a more sophisticated explanation that will help us both more.

 

[loveoforganic]

I'm pretty sure basicity only directly correlates to increased nucleophile strength when you're considering the same atom. e.g. LDA > diisopropyl amine, but not necessarily > isopropoxide

 

[matth87]

A good nucleophile wants to give up its negative charge.

A bad nucleophile is a good electrophile.
A good electrophile likes electrons or negative charges.
A good acid is a bad nucleophile, a weak base, and a good elctrophile.

In the examples in the book for SN1 reactions I think the weak nucleophile they use is actually H2SO4. Which is a strong acid, but can also be considered a weak base if you look at its conjugate.