Question

The reduction of carbonyl compounds by reaction with hydride reagents (H: \(^{-}\) ) and the Grignard addition by reaction with organomagnesium halides \(\left(\mathrm{R} \mathrm{R}^{-}{ }^{+} \mathrm{MgBr}\right)\) are examples of nucleophilic carbonyl addition reactions. What analogous product do you think might result from reaction of cyanide ion with a ketone?

Short answer

Reaction with cyanide ion produces a cyanohydrin.

Step-by-step solution

Understand Reaction Types

The question asks about nucleophilic addition reactions involving carbonyl compounds, specifically with cyanide ion. Recall that ketones undergo nucleophilic addition reactions where a nucleophile attacks the carbonyl carbon. Common reactions include hydride reduction (to alcohols) and Grignard addition (to tertiary alcohols).

Identify Reactants and Products

We start with a ketone, which has the general formula R2C=O. Here, the cyanide ion (CN⁻) is the nucleophile that will attack the carbonyl carbon, breaking the double bond.

Describe the Mechanism

The cyanide ion is a strong nucleophile and will attack the electrophilic carbon of the carbonyl group, resulting in the formation of a tetrahedral intermediate. This step involves the nucleophilic addition of CN⁻ to the carbonyl carbon.

Formulate the Product

After the addition of the cyanide ion, the resulting compound is a cyanohydrin. The former carbonyl oxygen can gain a hydrogen, completing the conversion. The general structure for a cyanohydrin is R₂C(OH)CN, where a hydroxyl group and cyanide are attached to the carbon.

Key concepts

carbonyl compounds

Carbonyl compounds are a significant class of organic molecules characterized by a carbon-oxygen double bond, expressed as C=O. This carbonyl group is present in several types of molecules, such as ketones and aldehydes. Each has its peculiarities and reactivity.

For instance:

• Ketones have the carbonyl group bonded to two carbon atoms. Their general formula is \( ext{R}_2 ext{C}=O\), where R represents alkyl groups.
• Aldehydes, on the other hand, feature the carbonyl group bonded to at least one hydrogen, depicted as \( ext{RCHO}\).

The remarkable characteristic of carbonyl compounds is their high reactivity, stemming from the polar nature of the carbonyl group.

The slight positive charge on the carbon atom makes it susceptible to attacks by nucleophiles—species which provide a pair of electrons. This is a fundamental basis for many reactions in organic chemistry, including the formation of alcohols and other valuable intermediates.

cyanide ion reaction

The cyanide ion (CN⁻) is a potent nucleophile and plays a critical role in nucleophilic addition reactions with carbonyl compounds. Due to its negative charge and relative stability, the cyanide ion is attracted to positively charged regions, such as the electrophilic carbon in carbonyl groups.

In these reactions:

• The cyanide ion approaches the carbon of the carbonyl group, which is partially positive due to the electronegativity of the oxygen atom.
• A tetrahedral intermediate forms when CN⁻ donates its electron pair to the carbon, effectively breaking the double bond between carbon and oxygen.

This process is key in synthesizing several organic compounds and intermediates. The versatility of the cyanide ion enables chemists to introduce cyanide into various molecular frameworks, which can be further transformed into carboxylic acids, amides, or amines depending on subsequent reactions.

Its reactivity with carbonyl groups exemplifies fundamental principles of nucleophilic addition mechanisms and expands the scope of synthetic methodologies in organic chemistry.

cyanohydrin formation

Cyanohydrin formation is a notable outcome of nucleophilic addition of the cyanide ion to carbonyl compounds. It is a two-step process that results in the transformation of a ketone or aldehyde into a cyanohydrin.

The steps include:

• The cyanide ion initially attacks the electrophilic carbon in the carbonyl group, as described previously.
• After the formation of a tetrahedral intermediate, a proton is added to the oxygen anion, usually from an external source, converting it into a hydroxyl group.

The resulting compound, called a cyanohydrin, has the general structure \( ext{R}_2 ext{C(OH)CN} \).

Cyanohydrins are important not only because they showcase a classic mechanism of organic synthesis but also because they serve as valuable precursors in producing various compounds. Indeed, the hydroxyl and nitrile groups present in cyanohydrins can undergo further chemical transformations, expanding the utility of this intermediates in synthetic pathways. This conversion demonstrates an efficient use of nucleophilic addition to build complexity in organic molecules.