Why does methanol have a higher boiling point than acetone?

Answer 1

Yes methanol has a far higher boiling point than methane. Methane is a gas at room temperature while methanol is a liquid. Alkanes such as butane have very low boiling points, while alcohols that have small R groups, have relatively high boiling points. The main reason for this phenomenon is than alcohols have Oxygen and Hydrogen in positions that make [Hydrogen Bonding http://en.wikipedia.org/wiki/Hydrogen_bond] possible.

Answer 2

Methanol is polar and with its -OH can form hydrogen bonds. Therefore its intermolecular forces are much stronger than the similarly sized oxygen. Intermolecular forces must be overcome in order to boil something, so methanol will have a higher boiling point. A quick note on the "similarly sized" comment I made. Whoever it was who assigned you this question wisely made it an easy comparison by chosing two compounds with the same number of electrons (16). There is a huge misconception that exists surrounding intermolecular forces----that molecules with hydrogen bonding or are polar always have stronger intermolecular forces than non-polar molecules. This simply isn't true. Non-polar molecules are held together by dispersion forces, temporary dipoles caused by shifting electron clouds, and unlike hydrogen bonding and polarity, dispersion forces scale with size. More electrons means more frequent and bigger fluctuations in the electron cloud and leads to stronger and stronger dispersion forces. This is why non-polar I2 with all its electrons is a solid, while methanol with its dispersion, dipole-dipole, and h-bonding forces is a liquid. By giving you two compounds with the same number of electrons, your teacher was basically requiring that the dispersion forces be comparable to each other, thus eliminating that as a variable. If you are using this to answer a homework question, you might want to talk about dispersion forces and how they are similar for these two compounds with the same number of electrons.

Answer 3

Methanol is an alcohol, which means it has an OH (hydroxyl) group attached to it, which allows it to form hydrogen bonds (a type of intermolecular interaction) with other molecules of methanol. These hydrogen bonds must be broken if you are to reach the boiling point of a liquid, and since hydrogen bonds are relatively strong, it takes more energy (heat) to break the bonds, resulting in a higher boiling point.

In comparison, the bromomethane molecule has a permanent dipole (bromine is far more electronegative than carbon, leading to a partial negative charge on the bromine atom and a partial positive charge on the carbon) which leads to dipole-dipole interactions (attractive forces between a positive region on one molecule and a negative region on another molecule) between bromomethane molecules. However, these dipole-dipole interactions are not as strong as hydrogen bonds, and therefore breaking them requires less energy input. This results in a lower boiling point.

Answer 4

methanol is more

polar than acetone so it evaporates much slowly than acetone and thus results in higher boiling point of methanol.