[hermione2884]

Why does 3-methylbutyl ethanoate have a higher boiling point than 3-methylbutan-1-ol and ethanoic acid? Is it because of its molar mass?

[AWK]

http://www.masterorganicchemistry.com/2010/10/25/3-trends-that-affect-boiling-points/

[thetada]

Mass indirectly affects boiling point because heavier atoms have more electrons, enabling them to form stronger instantaneous dipole induced dipole bonds (IDID). (Often referred to as Van der Waal forces.) However, other factors may outweigh the stronger IDID bonds of heavier atoms.

IDID bonds are an example of intermolecular forces and they exist between molecules of all three of the compounds you've listed.

Can you suggest what other intermolecular forces exist between molecules of each of the three compounds you've listed?

[hermione2884]

Ester: dispersion forces and dipole-dipole bonds
Alcohol:  dispersion forces and dipole-dipole bonds and hydrogen bonding
Carboxylic acid:  dispersion forces and dipole-dipole bonds and hydrogen bonding

[thetada]

Excellent. Now can you rank the strength of dispersion forces between molecules of each of the three compounds?

[hermione2884]

Based on dispersion forces ONLY (increasing order): carboxylic acid, alcohol, ester.

[thetada]

I agree, what's your reasoning?

[hermione2884]

I've ordered them based on increasing molar mass, i.e the ester has the largest molar mass.

[thetada]

OK, xenon has a greater mass than water but it is a gas at room temperature while water is a liquid. Consequently, comparing mass alone won't get full marks in exams. Mass indirectly correlates with boiling point because heavier particles contain more electrons.

So, rank the three compounds according to the total number of electrons contained in each.

How does the number of electrons affect dispersion forces and why?

How do intermolecular forces affect boiling point and why?

[Enthalpy]

Hydrogen bonds use to outweigh other factors, for instance at water compared with butane, but here they don't. Only the other contributions can explain that. The hard point is why more atoms outweigh the hydrogen bonds here.