Question

Arrange the following in decreasing order of nucleophilicity:
(A). H₂O
(B). NH₃
(C). OH⁻
(D). NH₂−
Choose the correct answer from the options given below:

• A. (A), (B), (C), (D)
• B. (D), (C), (B), (A)
• C. (B), (A), (D), (C)
• D. (D), (B), (C), (A)

Hint:

Nucleophilicity is the measure of the rate at which a species (nucleophile) will attack an electrophile, whereas basicity measures the thermodynamic stability of an atom. Generally, anions are stronger nucleophiles, and the higher the electronegativity, the lower the nucleophilicity.

Answer 1

The Correct Option is B

Nucleophilicity is the ability of a species to donate a lone pair to form a new bond. Factors like charge, electronegativity, and solvent affect nucleophilicity.
• Charge: Anionic species (OH-, NH2-) are stronger nucleophiles than neutral species (H2O, NH3), because of the high electron density resulting from the negative charge.
• Electronegativity: Within the same period, less electronegative atoms are better nucleophiles, for example N is less electronegative than O. NH2- is therefore a better nucleophile than OH-.
Therefore, the order of decreasing nucleophilicity is NH2- >OH->NH3>H2O