Can a strong nucleophile be a weak base?

Answer 1

Yes, a strong nucleophile can be a weak base.

In general, good bases are also good nucleophiles.

But weak bases can also be good nucleophiles. They fall into three classes.

i) Anions of large atoms

#"I"^-#, #"S"^(2-)#, and #"RS"^-# are good nucleophiles because they are large ions and their electron clouds are quite polarizable.

This means that they can start the bonding process while still some distance away from the substrate.

ii) Anions that are stabilized by resonance

The important members of this group are the carboxylate ions such as acetate ion (#"CH"_3"COO"^-#).

iii) Neutral bases that have lone pairs on less electronegative atoms

These include amines (#"RNH"_2#), thiols (#"RSH"#), and phosphines (#"RPH"_2#)

Of course, these bases are not as nucleophilic as the strong bases, but they are still strong nucleophiles.

The chart below lists the nucleophilicity of some common bases.

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Answer 2

Yes, a strong nucleophile can be a weak base. Nucleophilicity and basicity are related but distinct concepts. A compound can be a strong nucleophile due to its ability to donate a lone pair of electrons to form a new bond, yet be a weak base if it does not readily accept a proton. This can occur when the compound has other electron-donating groups that stabilize the resulting conjugate acid, reducing its tendency to accept a proton.

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.

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