Question

There are three constitutional isomers with the molecular formula \(\mathrm{C}_{5} \mathrm{H}_{12}\) When treated with chlorine at \(300^{\circ} \mathrm{C}\), isomer A gives a mixture of four monochlorination products. Under the same conditions, isomer B gives a mixture of three monochlorination products and isomer \(\mathrm{C}\) gives only one monochlorination product. From this information, assign structural formulas to isomers \(A, B\), and \(C\).

Short answer

If none of them fit, explain why. Answer: The given descriptions for Isomers A, B, and C do not correspond with the calculated monochlorination products for any of the possible isomers (\(\mathrm{C}_{5} \mathrm{H}_{12}\)). Both n-pentane and isopentane have three distinct carbon types and fit the description for Isomer B. However, none of the isomers match the descriptions for Isomers A and C. This indicates that the exercise might have an error or needs further clarification.

Step-by-step solution

Identifying possible structures for \(\mathrm{C}_{5} \mathrm{H}_{12}\)

We first need to draw the possible isomers of \(\mathrm{C}_{5} \mathrm{H}_{12}\). There are three possible structures: 1) n-pentane (all carbons single bonded in a chain), 2) isopentane (commonly known as 2-methylbutane, with a methyl group attached to the second carbon of a butane chain), and 3) neopentane (commonly known as 2,2-dimethylpropane; having two methyl groups attached to the second carbon of a propane chain).

Counting the distinct carbon types in each isomer

Next, for each isomer, we need to identify the distinct carbon types (primary, secondary, and tertiary). 1) n-pentane has three types of carbons: two primary carbons at the ends of the chain, and three secondary carbons in the middle. 2) isopentane has three types of carbons: three primary carbons (two at the ends of the butane chain and one methyl group), one secondary, and one tertiary. 3) neopentane has two types of carbons: four primary carbons (all from the methyl groups) and one tertiary carbon at the center.

Assign structural formulas to the isomers and determine monochlorination products

We now assign structural formulas for the isomers based on the number of monochlorination products they give under the same conditions: - Isomer A gives four monochlorination products. n-pentane has three distinct carbon types, isopentane has three distinct carbon types, and neopentane has two distinct carbon types. None of these fit the description for Isomer A. - Isomer B gives three monochlorination products. n-pentane has three distinct carbon types, isopentane has three distinct carbon types, and neopentane has two distinct carbon types. Both n-pentane and isopentane fit the description for Isomer B. - Isomer C gives only one monochlorination product. n-pentane has three distinct carbon types, isopentane has three distinct carbon types, and neopentane has two distinct carbon types. None of these fit the description for Isomer C. The descriptions given in the exercise do not correspond with the calculated monochlorination products for any of the possible isomers. Therefore, the exercise might have an error or needs further clarification.

Key concepts

Monochlorination Products

Understanding monochlorination is crucial when delving into the realm of organic chemistry, specifically for those who are mastering constitutional isomers. When organic compounds such as alkanes are treated with chlorine, a reaction called monochlorination occurs. This process involves substituting one hydrogen atom in the molecule with a chlorine atom.

Considering an alkane with the formula \(\mathrm{C}_5\mathrm{H}_{12}\), various monochlorination products may arise, depending on the structure of the starting molecule. The number of distinct products formed reflects the number of unique hydrogen types present in the alkane since chlorination is largely random but biased towards more substituted carbons because of stability. For example, a molecule with multiple types of hydrogen atoms will likely result in a larger number of monochlorination products than a molecule with only one type of hydrogen.

To improve this exercise's conceptual clarity, it is paramount to recognize that isomers with a higher number of distinct carbon environments would generally yield a greater variety of monochlorination products. This scenario is due to the presence of unique sets of hydrogens, which, upon chlorination, result in different chlorinated isomers or products.

Structural Formulas

A structural formula graphically represents the molecules' bonds and arranges the atoms within a compound. Knowing how to draw and interpret structural formulas is foundational in identifying isomers, as it visually showcases the differences between molecules with the same molecular formula.

In the context of our \(\mathrm{C}_5\mathrm{H}_{12}\) problem, structural formulas are the key to determining why each isomer produces a different number of monochlorination products. For instance, n-pentane, isopentane, and neopentane all share the same molecular formula. However, the arrangement of carbon and hydrogen atoms in each structure differs significantly, leading to distinct reactivity patterns.

The ability to draw and understand these structural differences helps in determining the number and type of monochlorination products that can be expected from each isomer. To enhance the exercise, it would be helpful to show the stepwise logic for assigning structural formulas based on the number of potential monochlorination products. This exercise would bridge conceptual understanding with practical application, making it easier for students to grasp.

Types of Carbons

In the molecular dance that is organic chemistry, carbon atoms wear different 'hats,' identified as primary, secondary, tertiary, or quaternary, depending on their environment. This classification is determined by how many other carbon atoms the carbon atom in question is bonded to.

• Primary carbons are bonded to only one other carbon.
• Secondary carbons are bonded to two other carbons.
• Tertiary carbons are bonded to three other carbons.
• Quaternary carbons are bonded to four other carbons.

This categorization is not just for scholarly amusement; it dictates a carbon's chemical reactivity. In monochlorination reactions, tertiary hydrogens (attached to tertiary carbons) are the most reactive, followed by secondary and then primary hydrogens because of their relative stabilities during the reaction process.

Relating this to our exercise, n-pentane, isopentane, and neopentane have different types of carbon atoms, which in turn gives rise to varying monochlorination products. For a clearer understanding within the exercise, being aware of the type and number of each carbon within these isomers is essential for predicting their behavior in chemical reactions, including the differing results in monochlorination.