Physical Properties of Alcohols

What alcohols are liquids at room temperature?

• Aliphatic alcohol (less than 12 carbons)

• Lower aryl alcohols

[Volatility] Why do alcohols have much higher b.p. compared to other organic compounds with similar Mr?

Alcohols have intermolecular hydrogen bonding (HB), thus greater amount of energy is needed to overcome the stronger intermolecular forces of attraction between the alcohol molecules. Hence, it is less volatile compared to other compounds.

What is the relationship between increasing no. of C in alcohol and its b.p.?

Th greater the the no, of C atoms, the higher the boiling point of alcohol

Why does boiling point increase with increasing C atoms?

Due to stronger intermolecular instantaneous dipole-induced dipole attractions (id-id) due to the increasing no. of electrons in the molecule.

What factor would cause b.p. to decrease?

Branching in isomers of alcohols

What is the relationship between the length of the carbon chain and it solubility in water?

Shorter chain alcohols are more miscible in water (as they form HB with H2O molecules)

Increasing C chain in alcohol causes solubility in water to decrease.

Why does longer carbon chain in alcohols decrease its solubility in H2O?

Hydrophobic nature increases; longer carbon chain causes the id-id attractions to dominate over the HB, causing the molecule to become more non-polar in nature.

Nature of Hydroxy Compounds

Amphoteric (weakly acidic and weakly basic)

Acid: Heterolytic fission between the O-H bonds

R-O←H —→ RO- + H+

(formation of alkoxide ion)

Basic: Heterolytic fission of C=O Bonds

R→O-H —→ R+ + OH-

(formation of carbocation)