Question:

The correct order of boiling points of N-ethylethanamine(I), ethoxyethane(II) and butan-2-ol(III) is

Updated On: Apr 26, 2025

III<II<I
II<III<I
II<I<III
III<I<II

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The Correct Option is C

Solution and Explanation

Detailed Explanation:

Boiling points are primarily influenced by the strength of intermolecular forces. The stronger the intermolecular forces, the higher the boiling point.

Ethoxyethane (II):
This is an ether. Ethers generally have weak dipole-dipole interactions and no hydrogen bonding between molecules. Thus, it has the lowest boiling point.
N-ethylethanamine (I):
This is a secondary amine. Amines can form hydrogen bonds due to the presence of –NH groups, but the hydrogen bonding in amines is weaker than in alcohols because nitrogen is less electronegative than oxygen. Therefore, it has a moderate boiling point.
Butan-2-ol (III):
Alcohols form strong hydrogen bonds due to the presence of the –OH group. Oxygen is highly electronegative, and the hydrogen bonding is strong, resulting in a high boiling point.

Order of Boiling Points: ethoxyethane < N-ethylethanamine < butan-2-ol

Correct Answer: (C): II < I < III

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Concepts Used:

Physical Properties - Alcohols, Phenols and Ethers

Alcohols, phenols, and ethers are organic compounds that exhibit a range of physical properties.

Physical Properties of Alcohols:

Alcohols are generally colorless, flammable liquids or solids with a characteristic odor. They have higher boiling points than hydrocarbons of comparable molecular weight due to hydrogen bonding between the hydroxyl groups. Alcohols also exhibit higher viscosity and surface tension than hydrocarbons. Alcohols are soluble in water due to the formation of hydrogen bonds between the hydroxyl groups and water molecules.

Physical Properties of Phenols:

Phenols are generally colorless to light pink or brown, crystalline solids with a distinctive odor. They have higher boiling points than hydrocarbons of comparable molecular weight due to hydrogen bonding between the hydroxyl groups. Phenols are less soluble in water than alcohols due to the lack of a second hydroxyl group for hydrogen bonding. They are, however, soluble in organic solvents.

Also Read: Physical and Chemical Properties of Alcohol

Physical Properties of Ethers:

Ethers are generally colorless, flammable liquids or gases with a characteristic odor. They have lower boiling points than alcohols of comparable molecular weight due to the absence of hydrogen bonding. Ethers are also less polar than alcohols and are less soluble in water. They are, however, more soluble in organic solvents than alcohols.

In summary, alcohols, phenols, and ethers exhibit a range of physical properties that depend on their molecular structure and functional groups. Understanding these physical properties is important for predicting the behavior of these compounds in various applications, such as in the production of solvents, fuels, and pharmaceuticals.