Predict which member of each pair has the higher boiling point, and explain the reasons for your predictions.
a. hexan-1-ol or 3,3-dimethylbutan-1-ol
b. hexan-2-one or hexan-2-ol

Verified step by step guidance

1. Step 1: Understand the factors affecting boiling points. Boiling points are influenced by intermolecular forces such as hydrogen bonding, dipole-dipole interactions, and London dispersion forces. Molecules with stronger intermolecular forces generally have higher boiling points.
2. Step 2: Analyze (a) hexan-1-ol vs. 3,3-dimethylbutan-1-ol. Both are alcohols, meaning they can form hydrogen bonds due to the presence of the hydroxyl (-OH) group. However, hexan-1-ol has a straight-chain structure, which allows for stronger London dispersion forces compared to the branched structure of 3,3-dimethylbutan-1-ol. Branching reduces the surface area available for intermolecular interactions, lowering the boiling point.
3. Step 3: Analyze (b) hexan-2-one vs. hexan-2-ol. Hexan-2-one is a ketone, which can only exhibit dipole-dipole interactions due to the polar carbonyl group. Hexan-2-ol, on the other hand, is an alcohol and can form hydrogen bonds in addition to dipole-dipole interactions. Hydrogen bonding is significantly stronger than dipole-dipole interactions, so hexan-2-ol is expected to have a higher boiling point.
4. Step 4: Compare molecular weights and structures. Both pairs of compounds have similar molecular weights, so the differences in boiling points are primarily due to the types and strengths of intermolecular forces rather than size.
5. Step 5: Summarize the predictions. For (a), hexan-1-ol is predicted to have a higher boiling point due to its straight-chain structure and stronger London dispersion forces. For (b), hexan-2-ol is predicted to have a higher boiling point due to the presence of hydrogen bonding, which is stronger than the dipole-dipole interactions in hexan-2-one.

Key Concepts

Hydrogen Bonding

Hydrogen bonding is a strong type of dipole-dipole interaction that occurs when hydrogen is bonded to highly electronegative atoms like oxygen or nitrogen. In alcohols, the presence of an -OH group allows for hydrogen bonding between molecules, significantly increasing their boiling points compared to hydrocarbons of similar molecular weight, which lack such interactions.

Molecular Structure and Steric Hindrance

Molecular structure refers to the arrangement of atoms within a molecule, which can influence physical properties like boiling point. Steric hindrance occurs when bulky groups around a functional group impede interactions, such as hydrogen bonding. In the case of 3,3-dimethylbutan-1-ol, the presence of two methyl groups near the -OH group reduces the ability to form hydrogen bonds compared to hexan-1-ol, leading to a lower boiling point.

Functional Groups and Polarity

Functional groups are specific groups of atoms within molecules that determine their chemical properties. The polarity of a molecule, influenced by its functional groups, affects its boiling point; polar molecules, like alcohols, generally have higher boiling points due to stronger intermolecular forces. In comparing hexan-2-one and hexan-2-ol, the alcohol's -OH group introduces polarity and hydrogen bonding, resulting in a higher boiling point than the ketone.