Question

Are all nucleophiles bases ?

Answer 1

Definition of a Base:

1. It is defined as a substance that is capable of donating a lone pair of electrons or accepting protons$\left({\mathrm{H}}^{+}\right)$ or donating hydroxide$\left({\mathrm{OH}}^{-}\right)$ ion in an aqueous solution.
2. Example: Sodium Hydroxide$\left(\mathrm{NaOH}\right)$, Sodium Hydride$\left(\mathrm{NaH}\right)$, Sodium Ethoxide$\left(\mathrm{NaOEt}\right)$.

Definition of a Nucleophile:

1. A nucleophile is a chemical species that is capable of donating lone pair of electrons or can react at electron-poor sites such as a proton.
2. Examples: Water$\left({\mathrm{H}}_2\mathrm{O}\right)$, Sodium ethoxide, Ammonia$\left({\mathrm{NH}}_3\right)$, Sodium Azide$\left({\mathrm{NaN}}_3\right)$

Explanation:

1. Thus, all the nucleophiles are Lewis bases because of their ability to donate lone pair of electrons.
2. Base or Bronsted base is a unique name of nucleophile when it attacks and forms a bond with a proton $\left({\mathrm{H}}^{+}\right)$.
3. Example: Sodium ethoxide can act as a base to abstract protons from water and can even act as a nucleophile in reaction with alkyl halides.
4. However, all nucleophiles can't act as base, for example ${\mathrm{I}}^{-}$ is a good nucleophile but not a good base.
5. However, all bases cannot be nucleophiles. Example: Lithium diisopropylamide or LDA $\left(\right[{\left({\mathrm{CH}}_3\right)}_2\mathrm{CH}{]}_2\mathrm{NLi})$ because it is very bulky, so an attack over electrophile will lead to a very sterically hindered system. Hence, such an attack is not possible, but instead, it can abstract proton easily and thus act as a good base.