Boiling Point Hierarchy (Similar Molar Mass)
Boiling Point Trend
Functional Group Boiling Point Hierarchy (Similar Molar Mass)
Carboxylic acid > Alcohol > Aldehyde / Ketone > Ester > Ether ≈ Alkane
- Carboxylic acids: Stable hydrogen-bonded dimers (2 H-bonds per pair).
- Alcohols: Extensive intermolecular hydrogen bonding.
- Carbonyls / Esters: Dipole-dipole attractions (polar C=O bond, no H-bonding between molecules).
- Alkanes: London dispersion forces only (weakest).
Factors Affecting Physical Properties
| Factor | Effect on BP | Reason |
|---|---|---|
| ↑ Chain length | Higher | More electrons → stronger LDFs |
| Branching | Lower | Smaller surface area → weaker LDFs |
| H-bonding groups (-OH, -NH₂) | Much higher | Strong IMFs between molecules |
Solubility
Solubility Rule
Chain Length and Aqueous Solubility
Short-chain alcohols, carboxylic acids, and amines (\(1\text{--}3\) carbons) are completely miscible with water because their polar functional groups form strong hydrogen bonds with water molecules.
As the non-polar hydrocarbon chain lengthens (\(\ge 4\) carbons), the hydrophobic effect dominates and water solubility decreases dramatically.
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