Arrange these five compounds in order of increasing boiling point: propan-1-ol, propanal, butane…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Arrange these five compounds in order of increasing boiling point: propan-1-ol, propanal, butane, propanone, methoxyethane. Their molar masses are close to . For each compound, name the strongest force that holds its molecules together. Then explain why propanone, and not propanal, is the more soluble in a large amount of water.
Need a reminder? The key ideaShow
The carbonyl carbon is and flat. Oxygen pulls the pi electrons, so carbon is and oxygen . An aldehyde is with the carbonyl carbon numbered 1. A ketone is and its carbonyl carbon gets the lowest number. Carbonyl compounds have dipole-dipole forces but no hydrogen bonds between their own molecules.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Step 1. Butane. It has only dispersion forces. It boils at , the lowest.
Step 2. Methoxyethane. An ether has a small dipole and no O-H group. It boils at .
Step 3. Propanal and propanone. The carbonyl dipole gives dipole-dipole forces. Propanal boils at and propanone at .
Step 4. Propan-1-ol. Its O-H group forms hydrogen bonds. It boils at , the highest.
Answer: butane, methoxyethane, propanal, propanone, propan-1-ol.
Watch out. The question about solubility has a trap. Both propanal and propanone can accept hydrogen bonds from water, so both dissolve well. Propanone is miscible with water in every ratio. Propanal dissolves well but not in every ratio.
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