Which of the following is the strongest nucleophile? OCH3 SCH3 CH3OH OC(CH3)3
The Correct Answer and Explanation is:
The strongest nucleophile among the options listed is SCH3 (methanethiolate).
Explanation:
Nucleophilicity refers to the ability of a molecule or ion to donate electrons to form a covalent bond with an electrophile. Several factors influence nucleophilicity:
- Size of the atom/ion: Larger atoms tend to be better nucleophiles because they can stabilize the negative charge more effectively.
- Charge: A negatively charged species is usually a stronger nucleophile than a neutral species because it has a higher electron density.
- Electron-donating groups: Substituents that donate electron density to the nucleophile (like alkyl groups) generally increase nucleophilicity.
- Solvent effects: Polar protic solvents can stabilize anions through hydrogen bonding, thus reducing nucleophilicity.
Analyzing the options:
- OCH3 (Methoxy): The oxygen is electronegative and holds a lone pair, but oxygen atoms are relatively small, which means that the negative charge is localized, making it less nucleophilic than sulfur.
- SCH3 (Methanethiolate): Sulfur is larger and more polarizable than oxygen, meaning it can better stabilize the negative charge. The sulfur atom also donates electrons more effectively, making it a stronger nucleophile than methoxy.
- CH3OH (Methanol): This is a neutral molecule, so it is a much weaker nucleophile compared to the negatively charged OCH3 and SCH3.
- OC(CH3)3 (Tert-butoxy): Although oxygen is electronegative and has a negative charge, the tert-butyl group is a bulky substituent, which increases steric hindrance. This reduces its nucleophilicity compared to the less hindered methoxy or thiolate groups.
Thus, SCH3 is the strongest nucleophile because of sulfur’s larger size, greater polarizability, and ability to stabilize the negative charge more effectively than oxygen.
