The correct order of boiling points for primary \(\left(1^{\circ}\right)\), secondary \(\left(2^{\circ}\right)\) and tertiary \(\left(3^{\circ}\right)\) alcohols is: (a) \(1^{\circ}>2^{\circ}>3^{\circ}\) (b) \(3^{\circ}>2^{\circ}>1^{\circ}\) (c) \(2^{\circ}>1^{\circ}>3^{\circ}\) (d) \(2^{\circ}>3^{\circ}>1^{\circ}\)

When studying the properties of alcohols, one of the most critical factors influencing their physical characteristics, such as boiling points, is hydrogen bonding. Alcohols consist of a hydroxyl group (-OH) attached to a carbon chain. The oxygen atom in this group is more electronegative than the hydrogen atom, creating a polar bond.

Because of this polarity, the lone pair of electrons on the oxygen can form a hydrogen bond with the hydrogen of another alcohol molecule's hydroxyl group. This interaction is a type of intermolecular force that is particularly strong compared to other kinds such as van der Waals forces. Hydrogen bonds require significant energy to break, leading to higher boiling points in substances where they are present.

Role of Hydrogen Bonding in Boiling Points

The more hydrogen bonds a molecule can form, the more energy it takes to vaporize it, hence the higher boiling point. In the context of primary, secondary, and tertiary alcohols, their capacity for hydrogen bonding varies, which in turn influences their boiling points. Primary alcohols can form the most hydrogen bonds, as they have two hydrogen atoms adjacent to the oxygen that can participate in bonding, leading to a higher boiling point.

The classification of alcohols into primary (1°), secondary (2°), and tertiary (3°) depends on the carbon atom to which the hydroxyl group is attached. This classification impacts their physical and chemical properties, including how they interact with other molecules.

Structural Differences Impacting Boiling Points

In a primary alcohol, the carbon with the hydroxyl group is connected to at least one more hydrogen atom, making two sites for hydrogen bonding. In secondary alcohols, the carbon attached to the -OH group is connected to two other carbon atoms and only one hydrogen atom, resulting in one site for hydrogen bonding. Tertiary alcohols, however, have no hydrogen atoms on the carbon with the hydroxyl group, which precludes them from forming hydrogen bonds at that site.

These structural differences directly influence boiling points. Primary alcohols, having the most opportunities for hydrogen bonding, typically exhibit the highest boiling points, followed by secondary alcohols, with tertiary alcohols usually having the lowest due to their inability to form intermolecular hydrogen bonds with similar strength.

Intermolecular forces (IMFs) are the forces of attraction or repulsion between molecules. Besides hydrogen bonding, several other types of IMFs affect the physical properties of substances.

Types of Intermolecular Forces

The key IMFs include London dispersion forces, dipole-dipole interactions, and hydrogen bonds. London dispersion forces are the weakest IMFs and occur momentarily due to the constant motion of electrons within and around molecules. Dipole-dipole interactions are stronger than London forces and occur between polar molecules where there is a permanent separation of charge.

Alcohols can exhibit all these types of IMFs, but it's the hydrogen bonding that is most impactful in determining their boiling points. The strength of these IMFs depends on the number of hydrogen bonds a molecule can form, as well as the overall polarity of the molecule. Stronger IMFs like hydrogen bonding require more energy—hence higher temperatures—to be overcome, which is why substances with these forces generally have higher boiling points.