Which one of the following compounds has the lowest boiling point?

Tertiary butyl chloride

The correct answer is option 2. Tertiary butyl chloride.

To determine which compound has the lowest boiling point among pentyl chloride, tertiary butyl chloride, isobutyl chloride, and n-butyl chloride, we need to understand the factors that influence boiling points:

Factors Affecting Boiling Point

Molecular Weight: Heavier molecules tend to have higher boiling points because they have stronger van der Waals forces.

Molecular Structure: More branched molecules have lower boiling points than their straight-chain isomers because branching reduces the surface area, leading to weaker van der Waals forces.

Intermolecular Forces: Stronger intermolecular forces (e.g., hydrogen bonding, dipole-dipole interactions, van der Waals forces) result in higher boiling points.

Analysis of the Compounds

1. Pentyl chloride (1-chloropentane, C₅H₁₁Cl):

Structure: Straight-chain alkyl chloride.

Molecular Weight: Relatively high among the options.

Boiling Point: Higher due to strong van der Waals forces resulting from its larger surface area.

2. Tertiary butyl chloride (2-chloro-2-methylpropane, (CH₃)₃CCl):

Structure: Highly branched molecule.

Molecular Weight: Lower than pentyl chloride.

Boiling Point: Lowest among the options due to extensive branching, which minimizes surface area and weakens van der Waals forces.

3. Isobutyl chloride (1-chloro-2-methylpropane, (CH₃)₂CHCH₂Cl):

Structure: Branched molecule, but less branched than tertiary butyl chloride.

Molecular Weight: Similar to n-butyl chloride.

Boiling Point: Higher than tertiary butyl chloride but lower than n-butyl chloride due to its intermediate level of branching.

4. n-Butyl chloride (1-chlorobutane, C₄H₉Cl):

Structure: Straight-chain alkyl chloride.

Molecular Weight: Lower than pentyl chloride but higher than tertiary butyl chloride. Boiling Point: Higher than isobutyl chloride and tertiary butyl chloride due to stronger van der Waals forces from its straight-chain structure.

Branching significantly lowers the boiling point because it reduces the surface area available for van der Waals interactions. Among the given compounds, tertiary butyl chloride is the most branched. Its highly compact structure results in the weakest van der Waals forces and the lowest boiling point.

Therefore, the compound with the lowest boiling point is: Tertiary butyl chloride