Which compound has the highest boiling point?
- An-Pentane
- BIsopentane
- CNeopentane
- DIsobutane
Solution & Step-by-step Explanation
Let's analyze the factors that determine the boiling points of alkanes:
Molecular Mass: Boiling point increases with an increase in molecular mass due to a greater number of electrons, which increases van der Waals attractive forces. Isobutane (C
4
H
10
) has a lower molecular mass than the pentane isomers (C
5
H
12
), so it has the lowest boiling point.
Branching Effects: For structural isomers with the same molecular formula (C
5
H
12
isomers), the boiling point decreases as branching increases. Branching changes the molecular shape from a linear chain to a spherical form, which reduces the surface area in contact with neighboring molecules and weakens intermolecular van der Waals forces.
Comparing the pentane isomers:
n-Pentane: Unbranched linear chain layout ⟹ Highest surface area ⟹ Highest boiling point.
Isopentane: Single branch layout ⟹ Intermediate surface area.
Neopentane: Highly branched spherical shape ⟹ Lowest surface area.
Molecular Mass: Boiling point increases with an increase in molecular mass due to a greater number of electrons, which increases van der Waals attractive forces. Isobutane (C
4
H
10
) has a lower molecular mass than the pentane isomers (C
5
H
12
), so it has the lowest boiling point.
Branching Effects: For structural isomers with the same molecular formula (C
5
H
12
isomers), the boiling point decreases as branching increases. Branching changes the molecular shape from a linear chain to a spherical form, which reduces the surface area in contact with neighboring molecules and weakens intermolecular van der Waals forces.
Comparing the pentane isomers:
n-Pentane: Unbranched linear chain layout ⟹ Highest surface area ⟹ Highest boiling point.
Isopentane: Single branch layout ⟹ Intermediate surface area.
Neopentane: Highly branched spherical shape ⟹ Lowest surface area.