Alcohol Properties Overview

Overview

This lecture covers the physical properties of alcohols, focusing on hydrogen bonding, solubility, and boiling point trends.

Alcohols contain an -OH (hydroxyl) group with a polar covalent bond (O partially negative, H partially positive).
This polar bond allows for dipole-dipole interactions and hydrogen bonding.

Alcohols form hydrogen bonds when the partially negative O aligns with the partially positive H of another molecule.
Hydrogen bonding is a strong intermolecular force, stronger than van der Waals or London dispersion forces.
Alcohols can hydrogen bond with water due to similar structure (HOH vs. ROH).

Alcohols are soluble in water due to hydrogen bonding between the -OH group and water.
Miscible means two liquids mix in any ratio to form a homogeneous solution.
Methanol and ethanol (small alcohols) are miscible with water.
As the nonpolar carbon chain increases, alcohols become less soluble in water (hydrophobic effect).

Small alcohols are hydrophilic (“water-loving”); longer carbon chains are hydrophobic (“water-fearing”).
The larger the hydrocarbon (carbon) portion relative to the -OH group, the less soluble the alcohol is in water.
For example, butanol is less soluble than ethanol because of its longer carbon chain.

Boiling point is the temperature needed to overcome intermolecular forces and turn a liquid into a gas.
Alcohols have higher boiling points than similar molecular weight compounds without hydrogen bonding (e.g., dimethyl ether).
Increasing the carbon chain (more carbons) increases boiling point due to stronger London dispersion forces.
Boiling point order (1 carbon to 4 carbons): methanol < ethanol < butanol.
Branching in the carbon chain lowers boiling point: straight-chain > secondary > tertiary alcohols.

Alcohol — Organic compound with an -OH (hydroxyl) group.
Hydrogen bonding — Strong intermolecular attraction between a hydrogen atom (bound to F, O, or N) and another electronegative atom.
Solubility — Ability of a substance to dissolve in a solvent.
Miscible — Liquids that combine in any proportion to form a homogeneous solution.
Hydrophilic — Water-loving, attracted to water.
Hydrophobic — Water-fearing, not attracted to water.
Boiling point — Temperature at which a liquid becomes a gas.

Review and understand hydrogen bonding and its effect on alcohol properties.
Study the relationship between carbon chain length, solubility, and boiling point.
Watch the next video on acid-base properties of alcohols.