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How do aldehyde melting and boiling points compare with hydrocarbons of similar molecular weight?
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aldehyde
Alcohols may be oxidized to give aldehydes, ketones, and carboxylic acids. The oxidation of organic compounds generally increases the number of bonds from carbon to oxygen, and it may decrease the number of bonds to hydrogen.
Aldehydes have considerably higher melting and boiling points than hydrocarbons of similar molecular weight.1
This difference is primarily due to the polarity of the carbonyl group found in aldehydes. Because aldehydes are polar molecules, they experience stronger intermolecular attractions than nonpolar hydrocarbons. Consequently, more energy—and thus a higher temperature—is required to separate these molecules during the processes of melting or boiling.1
For example, butane and propanal both have a molecular weight of 58. While the nonpolar hydrocarbon butane has a boiling point of 0 °C (32 °F), the polar aldehyde propanal has a significantly higher boiling point of 49 °C (120 °F).1