SolutionsPhysical and Bond Properties
1. Boiling points
Order from lowest to highest boiling point: propane, 1-propanol, 2-chloropropane and ethylene glycol.
Propane (−42 °C) < 2-chloropropane (36 °C) < 1-propanol (97 °C) < ethylene glycol (197 °C).
The dipole-dipole forces of the chloride raise the boiling point somewhat; the hydrogen bonds of the alcohol raise it much more, and with two OH groups even more.
2. Solubility in water
Why is methanol miscible with water in all proportions, while the solubility of 1-pentanol is only about 22 g/L?
The OH group forms hydrogen bonds with water, but the carbon chain is hydrophobic. In methanol the OH dominates; as the chain grows longer, the non-polar part weighs more and more and solubility decreases.
3. Branching
1-Butanol boils at 117 °C and 2-methyl-2-propanol at 82 °C. Why?
The tertiary alcohol is almost spherical: it has less contact surface between molecules (weaker London forces) and its more hindered OH forms hydrogen bonds less easily.
4. Hybridization
What is the hybridization of the oxygen of an alcohol? What C–O–H angle should we expect?
sp3, with two lone pairs. The C–O–H angle is about 109° (108.9° in methanol), close to tetrahedral.