Question

\(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{C} \equiv \mathrm{C}-\mathrm{CH}_{3}\) product The product formed is (a) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{CO} \mathrm{CH}_{3}\) (b) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CO} \mathrm{CH}_{2} \mathrm{CH}_{3}\) (c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CO} \mathrm{CO} \mathrm{CH}_{3}\) (d)

Short answer

a) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{CO}\mathrm{CH}_{3}\) b) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CO} \mathrm{CH}_{2}\mathrm{CH}_{3}\) c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CO} \mathrm{CO} \mathrm{CH}_{3}\) d) None of the above Answer: d) None of the above

Step-by-step solution

Given molecule is benzene ring attached with a triple bond on carbon and a methyl group. Remember that the functional group is added to the triple bond carbon. #Step 2: Evaluate each answer choice#

Now, let's evaluate each answer choice: (a) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CH}_{2} \mathrm{CO}\mathrm{CH}_{3}\) - This product has a ketone functional group (-CO-) added to the methyl group attached to benzyne. However, we should add the functional group to the triple bond carbon. (b) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CO} \mathrm{CH}_{2}\mathrm{CH}_{3}\) - This product has a ketone functional group (-CO-) added to the benzene ring and an ethyl group instead of a methyl group. This also doesn't represent the correct product. (c) \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{CO} \mathrm{CO} \mathrm{CH}_{3}\) - This product has two ketone functional groups attached to the benzene ring and a methyl group. This also doesn't represent the correct product. (d) None of the above - As none of the options represents the correct product after adding a functional group to the triple bond carbon, this answer is correct. So, the correct answer is (d) None of the above.

Key concepts

Alkyne Reactions

Alkynes, characterized by their carbon-carbon triple bonds, participate in a variety of chemical reactions due to their high reactivity. One fundamental reaction involving alkynes is the addition of functional groups across the triple bond. This addition can involve various reagents resulting in different products. For instance, alkynes can react with hydrogen in the presence of a metal catalyst (e.g., Pd, Pt, or Ni) to form alkenes in a process known as hydrogenation. If the hydrogenation continues, alkynes can be fully saturated to form alkanes.

Another common reaction is the addition of halogens, where an alkyne reacts with Br2 or Cl2 to form dihaloalkenes. In the presence of excess halogen, the alkyne can further react to form tetrahaloalkanes. Hydration of alkynes using water in the presence of acid and mercury(II) sulfate produces ketones or aldehydes, depending on the structure of the starting alkyne. It is essential to understand that the addition follows Markovnikov's rule, where the functional group attaches to the more substituted carbon atom.

Functional Group Addition

The addition of functional groups to multiple bonds, such as those present in alkenes and alkynes, is a cornerstone of organic chemistry transformations. This modification alters the physical and chemical properties of the original compound, making it a powerful tool for synthesizing a wide range of organic molecules.

During the functional group addition, electrophilic reagents tend to add to the most electron-rich site of a molecule. In alkyne chemistry, the typical addition reactions involve the transformation of the triple bond into single or double bonds by adding elements such as hydrogen, halogens, or hydroxyl groups. Specific conditions may favor the addition on one carbon over the other, leading to different isomers. This selectivity is guided by principles such as Markovnikov's and anti-Markovnikov's rules, wherein the more electronegative element or substituent usually adds to the carbon atom with fewer hydrogen atoms.

Benzene Derivatives

Benzene, a simple yet important aromatic compound, serves as a parent hydrocarbon for a wide variety of derivatives in organic chemistry. Benzene derivatives are formed when one or more hydrogen atoms of the benzene ring are replaced with other atoms or groups of atoms, known as substituents. These can include functional groups such as -OH (hydroxyl), -NO2 (nitro), -SO3H (sulfonic acid) and halogens like chlorine or bromine.

One key characteristic of benzene derivatives is their resonance stability due to the conjugated pi electron system within the ring. This resonance imparts unique properties in terms of their reactivity, often requiring stronger conditions for typical electrophilic addition reactions compared to alkenes or alkynes. Common reactions for forming benzene derivatives include nitration, sulfonation, halogenation, and Friedel-Crafts acylation or alkylation. Each reaction introduces a different functional group into the benzene ring, vastly expanding the complexity and utility of benzene-based compounds in organic synthesis.