Why the boiling point of aldehyde is lower as compare to alcohol?

Answer 1

Methanal is a gas (boiling point -21°C), and ethanal has a boiling point of +21°C. That means that ethanal boils at close to room temperature.

The other aldehydes and the ketones are liquids, with boiling points rising as the molecules get bigger.

The size of the boiling point is governed by the strengths of the intermolecular forces.

The aldehyde (with dipole-dipole attractions as well as dispersion forces) has a boiling point higher than the similarly sized alkane which only has dispersion forces. However, the aldehyde's boiling point isn't as high as the alcohol's. In the alcohol, there is hydrogen bonding as well as the other two kinds of intermolecular attraction:

molecule type boiling point (°C)
CH3CH2CH3alkane -42
CH3CHO aldehyde+21
CH3CH2OHalcohol +78

Answer 2

It is all about intermolecular forces. Looking at the structure of the two molecules, one can see that they both have london dispersion forces, as all molecules do, and they are both polar compounds and therefore possess dipole-dipole interactions. The alcohol, however, possesses a hydrogen on an electronegative atom unlike the aldehyde and can therefore form hydrogen bonds. Since the alcohol has more intermolecular forces at play keeping the molecules together, an alcohol molecule will be less likely to escape from the liquid phase to the gaseous phase, hence the higher boiling point than the aldehyde.

Answer 3

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For the first one, alcohols have the formula ROH, and I think you already should know water is HOH. And you should know why water has a higher boiling point then would expected. Now, for organic compounds, they will have hydrophobic and hydrophillic portions if they can be soluble in water. The larger the hydrophobic portion, the less solubility in water. Now for the third question. What is the major difference between alkanes, having only carbon and hydrogen atoms, and aldehydes and ketones? It is the oxygen, which imparts polar character, but will not ionize. For the last one, the lower the MW, the more volatile, assuming all other things are equal. But if you add functional groups that impart polarity, hydrogen bonding ability, etc., then boiling points will increase.

Answer 4

RE:
Why the boiling point of aldehyde is lower as compare to alcohol?

Answer 5

Acetaldehyde Boiling Point