What is the correct order of boiling points for Primary (1°), Secondary (2°) and Tertiary (3°) alcohols?

1° > 2° > 3°

The correct answer is option 1. 1° > 2° > 3°.

Let us delve into the details of why the boiling points of alcohols follow the order 1° > 2° > 3°.

Hydrogen Bonding:

The primary factor influencing the boiling points of alcohols is hydrogen bonding. Hydrogen bonding occurs when a hydrogen atom is directly bonded to a highly electronegative atom (like oxygen or nitrogen) and is attracted to another electronegative atom in a different molecule.

Primary Alcohols (1°):

In primary alcohols, the carbon atom bearing the hydroxyl (OH) group is attached to two hydrogen atoms. This allows for effective hydrogen bonding between alcohol molecules. The hydrogen bonding contributes to stronger intermolecular forces, requiring more energy to break these bonds and transition from the liquid to the gaseous phase (boiling)

Secondary Alcohols (2°):

In secondary alcohols, the carbon atom bearing the hydroxyl group is attached to one hydrogen atom. While secondary alcohols can still form hydrogen bonds, the reduced number of available hydrogen atoms decreases the strength and number of hydrogen bonds compared to primary alcohols

Tertiary Alcohols (3°):

In tertiary alcohols, the carbon atom bearing the hydroxyl group is not attached to any hydrogen atoms. As a result, tertiary alcohols exhibit the weakest hydrogen bonding among the three types. The absence of hydrogen atoms directly bonded to the carbon bearing the hydroxyl group limits the ability to form strong hydrogen bonds.

Boiling Point Trend:

Due to the varying strengths of hydrogen bonding, the boiling points follow the order: 1° > 2° > 3°. Primary alcohols have the highest boiling points because they can engage in more effective hydrogen bonding, requiring more energy for the transition to the gaseous phase. Secondary alcohols have intermediate boiling points, and tertiary alcohols have the lowest boiling points due to weaker hydrogen bonding.

In summary, the ability to form hydrogen bonds is a key factor influencing the boiling points of alcohols, and this trend is a result of the structural differences in primary, secondary, and tertiary alcohols.