Question

How do you rank nucleophiles?

Answer 1

First of all we should be aware of nucleophiles, their reactivity and their order of reactivity. In a chemical reaction Nucleophiles are electron rich species, which generally consists of an unshared pair of electrons, which they can donate. They generally attack a species which consists of positive center or positive charge. They are also known as electron donors. A good base is generally a good nucleophile.

Complete step-by-step answer: Types of nucleophiles:-
Halogens –.The anionic form of the halogens acts as a very good nucleophile, while its diatomic form does not exhibit any quality of a nucleophile.
For example ${I^ - }$ is the strongest nucleophile in a polar, protic solvent.
Carbon – In many organometallic reagents and also in enol form, the carbon acts as a nucleophile. There are various examples of compounds where the carbon acts as a nucleophile. For example – Grignard Reagent.
Oxygen – The hydroxide ion is a very good example of a nucleophile of oxygen. The other examples are - alcohols and hydrogen peroxide.
Sulphur – The best example where sulphur acts as a good nucleophile is Hydrogen Sulphide.
Nitrogen – The examples where nitrogen acts as nitrogen are – Amides, Ammonia, Azides and Nitrides.
The order of the nucleophilicity is just opposite to the order of basicity. The polarizability of the nucleophile is just related to the order of its nucleophilicity. The correct order of increasing of nucleophilicity is as follows:-

$RN{H_2}\, < \,\,OH\,\, < \,\,C{H_3}O\,\, < \,\,N{H_2}$

Note: The terms base and nucleophiles are different. All nucleophiles are generally Lewis which donates electron pairs, while the base is just given to a nucleophile which forms a bond with a proton. With the increase in density of negative charge, Nucleophilicity also increases