Introduction

Relevance of the Theme

"Chemistry is the art of decomposing substances and recomposing new substances from them and is a science whose tangible results are of great utility in society."

• Justus von Liebig

The solubility of organic compounds is one of the most important properties that allows us to understand and manipulate the reactivity of these substances. Being essential constituents of our daily life, these compounds are present in various states. Understanding the solubility of organic compounds in different solvents allows us to understand where and how these compounds can interact in our reality, whether in a medication, an industrial chemical substance, or even in our food.

Contextualization

The theme fits perfectly into the study of organic chemistry, as it is closely linked to the reaction processes and interactions of these substances. After studying the classification and basic characteristics of organic compounds, we reach an important stage: understanding how these substances behave in different environments. Solubility serves as a magnifying glass, allowing us to examine organic molecules and their interactions more closely. Furthermore, this theme establishes a solid foundation for future discussions on reactions of organic compounds, aiding in the interpretation of reaction mechanisms. In summary, the solubility of organic compounds is a crucial component of the study of organic chemistry that harmoniously links to other topics in the curriculum and, in turn, promotes a more comprehensive understanding of the subject.

Theoretical Development

Components

• Solubility of organic compounds: The ability to dissolve in a solvent is a characteristic of great relevance for organic compounds. This is crucial because, as we know, many chemical substances are transported in our body in an aqueous medium, demonstrating one of its practical applications. We will study the conditions that affect solubility, such as polarity, temperature, and pressure.

• Polarity of organic compounds: The polarity of a molecule is fundamental in determining whether it is soluble in a polar solvent (such as water) or in a nonpolar solvent (such as benzene). Polarity is influenced by molecular geometry and charge distribution. We will learn to identify the polarity of a molecule and how it affects solubility.

• Effect of functional groups: Functional groups, which are groups of atoms that possess specific chemical properties, can also affect the solubility of an organic compound. For example, the presence of a hydroxyl group (OH) in a compound generally increases its solubility in water due to the formation of hydrogen bonds. We will see how different functional groups affect solubility in different solvents.

Key Terms

• Solvent: Substance in greater quantity in the solution. In an organic compound, it can be either polar or nonpolar, depending on the characteristics of the molecule.
• Solution: Homogeneous mixture formed by a solute (dissolved compound) and a solvent.
• Solubility: Maximum amount of solute that can be dissolved in a fixed amount of solvent at a given temperature. It can be expressed in g/100 mL of solvent.
• Polar and nonpolar solutes: Compounds with significant differences in electronegativity between their atoms are polar, while compounds with similar electronegativities are nonpolar. The solubility of an organic compound depends on its polarity in relation to the solvent.

Examples and Cases

• Case 1 - Solubility of alcohols in water: Alcohols are organic compounds characterized by the presence of the hydroxyl group (OH). They have variable solubility in water, depending on the size of the carbon chain. Alcohols with one or two carbons are soluble in water due to their ability to form hydrogen bonds with water, while those with three or more carbons are insoluble because the organic portion is too large to effectively interact with water molecules.

• Case 2 - Solubility of hydrocarbons in water: Hydrocarbons, compounds formed only by carbon and hydrogen, are nonpolar and therefore insoluble in water. However, they can be soluble in nonpolar solvents such as benzene.

• Case 3 - Solubility of amines in water: Amines are organic compounds derived from ammonia (NH3), where one or more hydrogen atoms are replaced by organic groups. Since amines can form hydrogen bonds with water, their solubility increases with the number of amine groups present. For example, primary amine is more soluble in water than secondary amine, which is more soluble than tertiary amine.

These examples illustrate the importance of the solubility of organic compounds in various aspects of organic chemistry and how understanding the solubility of these compounds allows us to predict their behaviors and reactions.

Detailed Summary

Key Points

• Importance of Solubility: The solubility of organic compounds is a crucial property to be understood, as it establishes the basis for understanding how these substances can interact and react in different environments, leading to a better understanding and practical application of organic chemistry.

• Polarity: The polarity of an organic molecule is a critical factor that influences its solubility. If a molecule is polar, it will dissolve more easily in a polar solvent. If the molecule is nonpolar, it will tend to dissolve in a nonpolar solvent.

• Influence of Functional Groups: The functional groups present in organic compound molecules can directly affect their solubility, according to their nature and possible interactions with the solvent.

• Solubility and Carbon Chains: The size of the carbon chain can affect the solubility of an organic compound. Short-chain compounds can be soluble in water (if the functional group is hydroxyl, for example), while longer chains tend to be soluble in nonpolar solvents.

• Concepts: Solvent, Solution, Polar and Nonpolar Solutes, Solubility: These are fundamental terms that must be properly understood to comprehend the solubility of organic compounds.

Conclusions

• The polarity of a molecule, determined by its charge distribution, is one of the main reasons why a compound dissolves or not in a solvent.

• The solubility of organic compounds in water, a polar solvent, strongly depends on the presence and interaction of functional groups.

• The solubility of organic compounds in nonpolar solvents, such as hydrocarbons, mainly depends on the size of the carbon chain and the presence of polar or nonpolar functional groups.

Suggested Exercises

1. Explain, based on the concepts of solubility and polarity, why ethanol (C2H5OH) is soluble in water, while ethane (C2H6) is not.

2. Classify the solubility of the following compounds in water: propanal (CH3CH2CHO), propanone (CH3COCH3), propanol (CH3CH2CH2OH). Justify your answer considering the characteristics of polarity and interaction of functional groups.

3. Describe what happens, at a molecular level, when a compound with the carboxyl functional group (COOH) is introduced into water. How does this affect the solubility of the compound?