Which of the following bases would favorably deprotonate a hydroxyl group?
(c) NaCN

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Identify the pKa of the hydroxyl group. Hydroxyl groups typically have a pKa around 15-18, indicating the strength of the acid.

Determine the pKa of the conjugate acid of the base in question, NaCN. The conjugate acid of CN⁻ is HCN, which has a pKa of approximately 9.2.

Compare the pKa values: A base can deprotonate an acid if the pKa of the conjugate acid of the base is lower than the pKa of the acid being deprotonated.

Since the pKa of HCN (9.2) is lower than the pKa of the hydroxyl group (15-18), CN⁻ is a strong enough base to deprotonate the hydroxyl group.

Conclude that NaCN, which provides CN⁻ ions, can favorably deprotonate a hydroxyl group due to the relative acidity of HCN compared to the hydroxyl group.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Acid-Base Chemistry

Acid-base chemistry involves the transfer of protons between molecules. A base is a substance that can accept protons, while an acid is a substance that can donate protons. Understanding the strength of acids and bases is crucial for predicting the outcome of deprotonation reactions, where a base removes a proton from an acid.

pKa and Basicity

The pKa value of a compound indicates its acidity; lower pKa values correspond to stronger acids. Basicity refers to the ability of a base to accept protons. A base will favorably deprotonate a hydroxyl group if it is strong enough to overcome the hydroxyl's pKa, meaning the base must have a higher affinity for protons than the hydroxyl group.

Nucleophilicity of Cyanide Ion

The cyanide ion (CN-) is a strong nucleophile due to its negative charge and small size, which allows it to effectively attack electrophilic centers. In the context of deprotonation, CN- can act as a base, accepting protons from hydroxyl groups if the reaction conditions favor its basic properties over its nucleophilic tendencies.

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