Question

Trimethylamine, (CH₃)3N, has a small dipole, a formula mass of 59.1 u, and boils at 2.9 °C. Acetic acid, HC₂H₃O, has a large dipole, a formula mass of 60.1 u, and boils at 117.9 °C. Why is the boiling point of trimethylamine much lower than the boiling point of acetic acid?

Answer 1

Acetic acid has a higher boiling point than trimethylamine due to its ability to engage in stronger hydrogen bonding, owing to its larger dipole and the presence of a hydroxyl group.

Step-by-step explanation:

The reason acetic acid has a much higher boiling point than trimethylamine is because of the nature of the intermolecular forces (IMFs) each compound exhibits. Trimethylamine, (CH₃)₃N, while having a small dipole, boils at a lower temperature because it mainly experiences dispersion forces and some dipole-dipole interactions. On the other hand, acetic acid, HC₂H₃O₂, with a larger dipole and the presence of a hydroxyl group (-OH), can engage in hydrogen bonding, which is a particularly strong type of dipole-dipole interaction. This significant difference in the strength of IMFs leads to acetic acid having a much higher boiling point compared to trimethylamine.

Answer 2

The boiling point of trimethylamine is lower than that of acetic acid due to differences in their intermolecular forces (IMFs). Trimethylamine has weaker IMFs, while acetic acid has strong hydrogen bonding, resulting in a higher boiling point.

Step-by-step explanation:

The melting point and boiling point for methylamine are predicted to be significantly greater than those of ethane. CH3CH3 and CH3NH2 are similar in size and mass, but methylamine possesses an -NH group and therefore may exhibit hydrogen bonding. This greatly increases its intermolecular forces (IMFs), and therefore its melting and boiling points.

On the other hand, acetic acid has a large dipole due to the presence of the -COOH group, which results in strong hydrogen bonding. These stronger IMFs in acetic acid lead to a much higher boiling point compared to trimethylamine.