Question

\(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COCl}+\left(\mathrm{CH}_{3}\right)_{2} \mathrm{Cd} \rightarrow\) product \((\mathrm{s})\). The major organic product obtained is (a) \(\mathrm{CH}_{3} \mathrm{COCH}_{3}\) (b) \(\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{3}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COCH}_{2} \mathrm{CH}_{3}\) (d) \(\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}\)

Short answer

Answer: The major organic product of this reaction is (b) \(\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{3}\).

Step-by-step solution

Identify the reactants and the mechanism

The reactants in this reaction are \(\mathrm{CH}_{3} \mathrm{CH}_2 \mathrm{COCl}\) (an acyl chloride) and \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{Cd}\) (dimethylcadmium). The mechanism involved in the reaction is known as nucleophilic acyl substitution.

Identify the nucleophile and electrophile in the reaction

In this reaction, the nucleophile will be dimethylcadmium (\(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{Cd}\)), which can donate electrons to another molecule in the form of a methyl group \(\mathrm{CH}_{3}\). The electrophile will be the acyl chloride (\(\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{COCl}\)), which can accept electrons due to the high electrophilicity of the carbonyl carbon in the acyl chloride.

Perform the nucleophilic acyl substitution

In the nucleophilic acyl substitution, the methyl group from the nucleophile dimethylcadmium will attack the electrophilic carbonyl carbon of the acyl chloride, causing the carbonyl group to reform and the chloride to be expelled as a leaving group. The final major organic product of this reaction is formed, \(\mathrm{CH}_{3}\mathrm{COCH}_{2}\mathrm{CH}_{3}\).

Select the correct answer among the given options

Now that we know the product of this reaction, we can compare it to the given options. The correct answer is (b) \(\mathrm{CH}_{3} \mathrm{COCH}_{2} \mathrm{CH}_{3}\), as this is the major organic product obtained from the nucleophilic acyl substitution.

Key concepts

Organic Reaction Mechanisms

Understanding organic reaction mechanisms is essential for mastering organic chemistry. A reaction mechanism is a step-by-step description of how a chemical reaction occurs at the molecular level. It includes the breaking and forming of chemical bonds, rearrangements of atoms, and the intermediates that are formed during the progression of the reaction.

In the context of the exercise provided, the reaction mechanism in question is nucleophilic acyl substitution. This particular mechanism is important as it describes the process by which a nucleophile replaces a leaving group in a compound with an acyl group, a common functional group in organic compounds. The replacement of the chloride by a methyl group in the exercise is a prime example of this mechanism.

To enhance the learning process, it is beneficial to visualize reaction mechanisms through reaction arrows that show the movement of electrons, draw intermediate structures, and identify where bonds are formed or broken. These steps foster a deeper understanding of the intricate dance of electrons that constitutes the very essence of chemical reactions.

Acyl Chloride Reactivity

Acyl chlorides (acid chlorides) represent a class of organic compounds known for their high reactivity. This reactivity is driven by two primary factors: the high electrophilicity of the carbonyl carbon and the good leaving group ability of the chloride ion.

The electrophilicity comes from the polarization of the carbonyl bond, with the carbon being positive and the oxygen being negative. As a result, the carbonyl carbon is very susceptible to attack by nucleophiles. Additionally, the chlorine atom is connected to the carbonyl carbon and due to its high electronegativity, it can easily depart with its bonding electrons, making the acyl chloride an excellent compound for substitution reactions.

When approaching exercises involving acyl chlorides, familiarity with their reactivity patterns allows for better predictions of the outcome of reactions. It is also important to note that acyl chlorides react with various nucleophiles, including amines, alcohols, and even organometallic compounds, leading to a variety of products.

Nucleophile and Electrophile Identification

The identification of nucleophiles and electrophiles is a foundational skill in understanding organic reactions. Nucleophiles are species that are rich in electrons and are attracted to positive or partially positive atoms, where they can donate electrons. They often possess lone pairs or pi bonds that enable them to form new bonds with electrophiles.

Electrophiles, on the other hand, are electron-poor species that have a positive or partial positive charge, making them seek out electrons to gain stability. They are characterized by a deficiency of electrons and can accept electron pairs from nucleophiles.

In the solved exercise, dimethylcadmium is a nucleophile since it donates a methyl group to the carbonyl carbon of the acyl chloride. Acyl chloride is the electrophile because of its carbonyl carbon's susceptibility to nucleophilic attack. This interaction is the core of the nucleophilic acyl substitution mechanism. Students should practice identifying these reaction participants in various organic compounds to sharpen their problem-solving skills and deepen their understanding of reaction mechanisms.