Problem 59 - Chemistry: An Atoms-Focused Approach

Question

Which of the following compounds is the most soluble in water? a. \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{O}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{CH}_{3}\) b. \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{3} \mathrm{O}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{CH}_{3}\) c. \(\mathrm{CH}_{3} \mathrm{OCH}_{3}\) d. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OCH}_{2} \mathrm{CH}_{3}\)

Step-by-Step Solution

Answer

Answer: Compound c is the most soluble in water.

Step 1: Identifying Polar and Non-Polar Regions

In each of the given compounds, the oxygen atom creates a polar region within the molecule because oxygen is more electronegative than carbon and hydrogen. The remaining parts of each compound are mostly non-polar CH regions. Now let's analyze each of the given compounds based on their polar and non-polar regions.

Step 2: Compound a

The given structure of compound a is \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{2}\mathrm{O}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{CH}_{3}\). This compound has a non-polar region with a total of 6 CH units.

Step 3: Compound b

The given structure of compound b is \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{3}\mathrm{O}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{CH}_{3}\). This compound has a non-polar region with a total of 8 CH units.

Step 4: Compound c

The given structure of compound c is \(\mathrm{CH}_{3} \mathrm{OCH}_{3}\). This compound has a non-polar region with a total of 1 CH unit.

Step 5: Compound d

The given structure of compound d is \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OCH}_{2} \mathrm{CH}_{3}\). This compound has a non-polar region with a total of 4 CH units.

Step 6: Identifying the Most Soluble Compound in Water

Since water is a polar solvent, the compound with the least non-polar CH units will have the greatest solubility in water. Among the given compounds, compound c has the least non-polar_CH_units (only 1 CH unit). Therefore, compound c (\(\mathrm{CH}_{3} \mathrm{OCH}_{3}\)) is the most soluble in water.

Key Concepts

Polar and Non-Polar Regions

In organic compounds, molecules are usually divided into polar and non-polar regions, which describe the type of interactions they can have. Polar regions are parts of the molecule where polar bonds occur. These bonds happen when atoms with different electronegativities bond together. For example, an oxygen atom in a compound typically creates a polar region because oxygen is more electronegative than most other elements, drawing electrons toward itself.
Non-polar regions usually consist of hydrocarbon chains where the electronegativity difference between carbon and hydrogen is small. These non-polar parts do not attract water molecules as strongly. Understanding these regions helps in predicting how molecules interact with solvents like water.

Solubility in Water

The solubility of an organic compound in water largely depends on the presence and proportion of polar and non-polar regions. Water, being a polar solvent, is excellent at dissolving ionic compounds and molecules that have significant polar regions. This is because similar polar molecules are attracted to each other.

• Compounds with more polar parts tend to be more soluble in water.
• Those with larger non-polar regions are less soluble.

For the given exercise, determining which compound is most soluble in water involves assessing how many non-polar parts each compound has. The fewer non-polar regions, the higher the solubility. For instance, compound c, which has the smallest non-polar region among the options, is the most soluble in water.

Organic Chemistry

Organic chemistry focuses on the study of carbon-containing compounds. These compounds can vary drastically in terms of their structure and properties. In the study of solubility, organic chemists often look at the balance between polar and non-polar elements within a molecule, as these influence how a compound interacts with different solvents.
Through various techniques, chemists determine the solubility of an organic compound by considering how the structure, functional groups, and type of bonds affect its overall nature. This analysis helps in numerous applications, from creating pharmaceuticals to developing new materials.

Oxygen Electronegativity

Oxygen's position on the periodic table makes it one of the more electronegative elements, meaning it has a strong tendency to attract electrons in a chemical bond. This characteristic heavily influences the polarity of molecules in which oxygen atoms participate.

• Molecules containing oxygen often have polar bonds because oxygen pulls shared electrons, creating a dipole.
• This dipole moment results in polar regions, critical for solubility in polar solvents like water.

In the context of the exercise, the presence of oxygen in these organic compounds creates a pivotal polar region, despite the non-polar hydrocarbon chains. This results in the notable solubility differences seen among the compounds.