The product P formed in the following reaction is \(\mathrm{C}_{6} \mathrm{H}_{6}+\mathrm{CH}_{2}=\mathrm{CH}-\mathrm{CH}=\mathrm{CH}_{2} \stackrel{\mathrm{HF}}{\stackrel{0^{\circ} \mathrm{C}}}{\longrightarrow} \mathrm{P}\) (a) \(\mathrm{C}_{6} \mathrm{H}_{5}-\mathrm{CH}_{2}-\mathrm{CH}=\mathrm{CH}-\mathrm{CH}_{3}\) (b) \(\mathrm{C}_{6} \mathrm{H}_{5}-\mathrm{CH}=\mathrm{CH}_{2}\) (c) CC=C(C)CCC (d) \(\mathrm{C}_{6} \mathrm{H}_{5}-\mathrm{CH}_{2}-\mathrm{CH}_{2}-\mathrm{CH}=\mathrm{CH}_{2}\)

Benzene is one of the fundamental compounds in organic chemistry, known for its stability and unique structure consisting of a ring with six carbon atoms, each bonded to a hydrogen atom. Its reactions often involve the preservation of the aromatic system, which contributes to its stability.

One common type of reaction benzene undergoes is called electrophilic aromatic substitution (EAS), where an electrophile substitutes a hydrogen atom on the ring. However, in certain conditions, benzene can also participate in addition reactions, which are less common. In the exercise, benzene reacts in an electrophilic addition reaction, which is not typical, because benzene usually resists adding groups to its structure to preserve its aromaticity.

In this exception, benzene acts as a nucleophile due to the presence of an acetylene molecule and the catalyst hydrogen fluoride at 0°C, allowing the addition reaction to proceed. This is an important distinction as it hints at the selectivity and conditions required for benzene to undergo such reactions, showing that under the right circumstances, even the most stable aromatic rings can be prompted to react.

Understanding the reaction mechanism is crucial for predicting the outcome of a chemical reaction. A reaction mechanism is a step-by-step account of the path taken by electrons as reactants transform into products.

In the provided exercise, the mechanism involves a sequence of steps starting with the creation of a reactive intermediate. This intermediate is formed when acetylene employs its pi electrons to perform a nucleophilic attack on hydrogen fluoride, a process facilitated by the strong acidic conditions. The reaction proceeds with the generation of a carbocation that is highly electrophilic.

The next critical step is the nucleophilic attack by benzene on this carbocation, resulting in the formation of a new carbon-carbon bond. To restore its aromaticity, the benzene ring donates a hydrogen atom, symbolizing the importance of regaining stability in aromatic compounds. It's this methodical approach to understanding each step that allows chemists to predict and eventually confirm the final structure of the product.

Nucleophilic attack is a fundamental concept in organic chemistry, where a nucleophile, which is a species rich in electrons, targets a positively charged or electron-deficient site on another molecule, known as an electrophile.

The key to a successful nucleophilic attack is the presence of a good nucleophile, often bearing a negative charge or lone pairs of electrons ready to be shared. In our exercise, the first nucleophilic attack occurs when acetylene, acting as a nucleophile, reacts with hydrogen fluoride. This leads to the formation of the vinyl fluoride intermediate after the donation of electrons to the electrophilic center.

Importance of the Intermediate

Understanding intermediate formation is crucial, as it guides the subsequent steps of the reaction. Intermediates often determine the direction and outcome of a chemical reaction. The second nucleophilic attack involves the benzene ring targeting the carbocation, showcasing the direct interaction between the nucleophile and electrophile. The fundamental knowledge of these interactions is vital for those studying organic chemistry, as it forms the basis for synthesizing a broad range of compounds in both industrial and research settings.