Table of contents

1. A Review of General Chemistry5h 5m
2. Molecular Representations1h 14m
3. Acids and Bases2h 46m
4. Alkanes and Cycloalkanes4h 17m
5. Chirality3h 39m
6. Thermodynamics and Kinetics1h 22m
7. Substitution Reactions1h 48m
8. Elimination Reactions2h 30m
9. Alkenes and Alkynes2h 9m
10. Addition Reactions3h 19m
11. Radical Reactions1h 58m
12. Alcohols, Ethers, Epoxides and Thiols2h 42m
13. Alcohols and Carbonyl Compounds2h 17m
14. Synthetic Techniques1h 26m
15. Analytical Techniques:IR, NMR, Mass Spect7h 3m
16. Conjugated Systems6h 13m
17. Ultraviolet Spectroscopy51m
18. Aromaticity2h 34m
19. Reactions of Aromatics: EAS and Beyond5h 1m
20. Phenols55m
21. Aldehydes and Ketones: Nucleophilic Addition4h 56m
22. Carboxylic Acid Derivatives: NAS2h 51m
23. The Chemistry of Thioesters, Phophate Ester and Phosphate Anhydrides1h 10m
24. Enolate Chemistry: Reactions at the Alpha-Carbon1h 53m
25. Condensation Chemistry2h 9m
26. Amines1h 43m
27. Heterocycles2h 0m
28. Carbohydrates5h 53m
29. Amino Acids4h 20m
30. Peptides and Proteins2h 42m
31. Catalysis in Organic Reactions1h 30m
32. Lipids 2h 50m
33. The Organic Chemistry of Metabolic Pathways2h 52m
34. Nucleic Acids1h 32m
35. Transition Metals6h 14m
36. Synthetic Polymers1h 49m

2. Molecular Representations

How To Determine Solubility

Organic Chemistry

2. Molecular Representations

How To Determine Solubility

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Problem 75

Textbook Question

Why are lower molecular weight alcohols more soluble in water than higher molecular weight alcohols?

Verified step by step guidance

Consider the structure of alcohols: they have a hydrophilic (water-attracting) hydroxyl group (-OH) and a hydrophobic (water-repelling) hydrocarbon chain.

Understand that solubility in water is influenced by the ability of a substance to form hydrogen bonds with water molecules.

Recognize that lower molecular weight alcohols have shorter hydrocarbon chains, which means the hydrophilic hydroxyl group has a more significant influence on the molecule's overall polarity.

Note that as the hydrocarbon chain length increases in higher molecular weight alcohols, the hydrophobic character of the molecule increases, reducing its overall solubility in water.

Conclude that the balance between the hydrophilic and hydrophobic parts of the molecule determines the solubility, with lower molecular weight alcohols being more soluble due to their relatively larger hydrophilic component.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Hydrophilicity and Hydrophobicity

Hydrophilicity refers to the affinity of a molecule for water, while hydrophobicity indicates a lack of such affinity. Lower molecular weight alcohols, like methanol and ethanol, have shorter hydrocarbon chains, which makes them more hydrophilic due to their ability to form hydrogen bonds with water. In contrast, higher molecular weight alcohols have longer hydrophobic hydrocarbon chains that reduce their overall solubility in water.

Hydrogen Bonding

Hydrogen bonding is a type of intermolecular force that occurs when a hydrogen atom covalently bonded to a highly electronegative atom, such as oxygen, interacts with another electronegative atom. Lower molecular weight alcohols can form more hydrogen bonds with water molecules due to their smaller size and higher proportion of hydroxyl (-OH) groups, enhancing their solubility. Higher molecular weight alcohols have fewer hydroxyl groups relative to their size, limiting their ability to interact with water.

Molecular Size and Structure

The size and structure of a molecule significantly influence its solubility in water. As the molecular weight of alcohols increases, the hydrophobic hydrocarbon portion becomes more dominant, overshadowing the hydrophilic -OH group. This structural change leads to decreased solubility in water for higher molecular weight alcohols, as the larger hydrophobic regions do not interact favorably with water molecules.

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Textbook Question

Which of the following reactions would benefit from micellar technology (Figure 7.10), allowing them to be run in water?

(a)

(b)

(c)

Textbook Question

The effectiveness of a barbiturate as a sedative is related to its ability to penetrate the nonpolar membrane of a cell. Which of the following barbiturates would you expect to be the more effective sedative?

Textbook Question

Explain why amino acids, unlike most amines and carboxylic acids, are insoluble in diethyl ether.

Textbook Question

Ansaid and Motrin belong to the group of drugs known as nonsteroidal anti-inflammatory drugs (NSAIDs). Both are only slightly soluble in water, but one is a little more soluble than the other. Which of the drugs has the greater solubility in water?

Textbook Question

Which has

c. the greater solubility in water: 1-butanol or 1-pentanol?

d. the higher boiling point: 1-hexanol or 1-methoxypentane?

Textbook Question

Rank the following molecules from least water soluble to most water soluble. Explain your reasoning.

(e) CH₃CH₂CH₂CH₂CH₃

Textbook Question

In each pair, (i) choose the compound that is most soluble in water. (ii) Within each pair, which is most soluble in nonpolar solvents?

(a)

Multiple Choice

Which of the following substances is considered hydrophobic?