Question

Write a structural formula (one for each part) that fits the following descriptions. (These descriptions can apply to more than one structural formula.) a. A liquid basic nitrogen compound of formula \(\mathrm{C}_{3} \mathrm{H}_{7} \mathrm{~N}\) with \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{SO}_{2} \mathrm{Cl}\) and excess \(\mathrm{NaOH}\) solution gives a clear solution. This solution when acidified gives a solid product of formula \(\mathrm{C}_{9} \mathrm{H}_{11} \mathrm{O}_{2} \mathrm{NS}\). b. A liquid diamine of formula \(\mathrm{C}_{5} \mathrm{H}_{14} \mathrm{~N}_{2}\) with \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{SO}_{2} \mathrm{Cl}\) and \(\mathrm{NaOH}\) gives an insoluble solid. This solid dissolves when the mixture is acidified with dilute hydrochloric acid.

Short answer

a. Propylamine (\( \mathrm{CH}_3\mathrm{CH}_2\mathrm{CH}_2\mathrm{NH}_2 \)); b. Piperazine.

Step-by-step solution

Analyze Given Data for Part A

Part A describes a basic nitrogen compound with the formula \( \mathrm{C}_{3} \mathrm{H}_{7} \mathrm{~N} \). It reacts with \( \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{SO}_{2} \mathrm{Cl} \) and excess \( \mathrm{NaOH} \) to form a solution, and upon acidification, produces a solid \( \mathrm{C}_{9} \mathrm{H}_{11} \mathrm{O}_{2} \mathrm{NS} \). This implies the compound is likely an amine, as it forms a sulfonamide which is commonly isolated as a solid during such reactions.

Determine Structural Formula for Part A

The compound described in Part A is likely propylamine (CH3CH2CH2NH2). This primary amine can react with \( \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{SO}_{2} \mathrm{Cl} \) to form the sulfonamide \( \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{SO}_{2} \mathrm{NHCH}_2\mathrm{CH}_2\mathrm{CH}_3 \), which fits the molecular formula \( \mathrm{C}_{9} \mathrm{H}_{11} \mathrm{O}_{2} \mathrm{NS} \) when acidified.

Analyze Given Data for Part B

Part B describes a diamine with the formula \( \mathrm{C}_{5} \mathrm{H}_{14} \mathrm{~N}_{2} \). It reacts with \( \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{SO}_{2} \mathrm{Cl} \) and \( \mathrm{NaOH} \) to form an insoluble solid that becomes soluble upon acidification with hydrochloric acid. This behavior is characteristic of secondary amines, where only one amino group reacts with the sulfonyl chloride, leaving the other free.

Determine Structural Formula for Part B

The compound described in Part B is likely piperazine (\( \mathrm{N}\)-substituted ethylenediamine ring), a secondary diamine. It can form a p-toluenesulfonamide with one \( \mathrm{C}_{6} \mathrm{H}_{5} \mathrm{SO}_{2} \mathrm{Cl} \), which is sparingly soluble in water but dissolves in acidic solutions due to protonation of the remaining amine.

Key concepts

Structural Formula

In organic chemistry, a structural formula is a way to represent the connectivity between atoms in a molecule. Unlike molecular formulas, which simply list the number and type of atoms present, structural formulas provide a visual representation of the molecule's layout, showing how the atoms are linked.
For example, the structural formula for propylamine, involved in part A of the exercise, would be written as CH3-CH2-CH2-NH2. This formula tells us not only which atoms are present, but also how they are connected to form the amine.
Similarly, in part B, the structural formula for piperazine indicates a circular arrangement with nitrogen atoms in the ring. These structures are crucial for understanding the reactivity and physical properties of the molecules.
When drawing structural formulas, it is essential to consider the valent atomic connections and their order to ensure a correct and chemically meaningful representation.

Amines

Amines are organic compounds that contain an amino group, \(\text{RNH}_2\), where \(\text{R}\) typically stands for any carbon-containing group. They are derived from ammonia and are basic, meaning they can accept protons. The basicity comes from the presence of a lone pair of electrons on the nitrogen atom, available for bonding.
In this exercise, propylamine and piperazine are examples of an amine and a diamine, respectively. Propylamine reacts with sulfonyl chloride ( \(\text{C}_6\text{H}_5\text{SO}_2\text{Cl}\)) to form a sulfonamide, demonstrating typical characteristics of amines.
Amines are versatile compounds used in various applications, including pharmaceuticals and agriculture, due to their ability to form a variety of derivatives.

Sulfonamides

Sulfonamides are a class of compounds that arise when a sulfonyl group connects to an amine group, creating a sulfonamide link. They are characterized by the presence of \(\text{R}_2\text{N}\text{SO}_2\text{R'}\) structure. These compounds are commonly used in drugs due to their antibacterial properties.
The exercise involves the creation of sulfonamides from amines. In part A, the interaction of propylamine with sulfonyl chloride leads to the formation of a sulfonamide, which, upon acidification, becomes insoluble.
The ability of sulfonamides to interact with biological systems is largely due to their structural similarity with naturally occurring substrates, which makes them effective in therapeutic interventions.

Chemical Reactions

Chemical reactions, in the context of organic chemistry, involve the transformation of one set of chemical substances to another. Such reactions often involve electron pair sharing or transfer, resulting in new bonds being formed and some broken.
In the provided exercise, two reactions illustrate typical organic transformations: the formation of sulfonamides from amines using sulfonyl chloride. This involves nucleophilic substitution, where an amine group from the nitrogen compound substitutes for the chlorine in sulfonyl chloride, forming a new compound.
Another key reaction feature is acid-base behavior: the insolubility and solubility change of compounds when treated with acids or bases. This behavior helps identify the presence of certain functional groups in unknown compounds and is a fundamental concept in organic chemistry.