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The equilibrium constant, denoted as \( K_{eq} \), is a crucial concept in chemical reactions. It measures the ratio of the concentration of products to reactants at equilibrium.
In cyanohydrin formation, the equilibrium constant determines how far the reaction proceeds towards forming the cyanohydrin product.
When sodium cyanide (NaCN) is used instead of hydrogen cyanide (HCN), the concentration of cyanide ions \( (\text{CN}^-) \) increases due to the full dissociation of NaCN in water. According to Le Chatelier's principle, adding more reactants will shift the equilibrium towards the products, potentially increasing \( K_{eq} \).
However, the production of hydroxide ions \( (\text{OH}^-) \) with NaCN adds basicity to the solution. This can react with hydronium ions \( (\text{H}^+) \), possibly tipping the equilibrium back towards the reactants.
The balance between these factors—added cyanide ions and increased basicity—will determine whether the equilibrium constant is more or less favorable in the NaCN scenario compared to using HCN.

Carbonyl compounds, characterized by the carbon-oxygen double bond \( (\text{C=O}) \), play a central role in the cyanohydrin reaction. In this case, 2-propanone (acetone) acts as the carbonyl compound.
The carbon in the \( (\text{C=O}) \) group is electrophilic due to the electronegativity of the oxygen atom. This makes it a target for nucleophilic attack by cyanide ions \( (\text{CN}^-) \).
Upon attack, the carbonyl carbon forms a bond with the cyanide ion, and the double bond between carbon and oxygen becomes a single bond, with oxygen gaining an additional hydrogen to form a hydroxyl (OH) group.
These interactions convert the carbonyl compound into a cyanohydrin \( (\text{R}_2\text{C(OH)CN}) \), showcasing the transformation capacity of the carbonyl group in creating complex products.

A nucleophile is a species that donates an electron pair to form a chemical bond in reaction. In the cyanohydrin reaction, the cyanide ion \( (\text{CN}^-) \) serves as the nucleophile.
Cyanide ions are negatively charged, making them attractively paired to the partial positive charge on the electrophilic carbon in the carbonyl group.
The reactivity of nucleophiles can determine the course and success of a reaction. For cyanohydrins, using NaCN results in a higher concentration of cyanide ions present in the solution compared to HCN presence. This potentially increases the likelihood of the nucleophile reacting with the carbonyl compound.
Understanding the role of nucleophiles like cyanide is crucial to predicting reaction outcomes, as well as manipulating reaction conditions to achieve desired products efficiently. By choosing the right nucleophile and conditions, chemists can control the path and efficiency of chemical transformations.