HardChemistryHigh School (11–12)Organic Compounds with Functional Groups › Aldehydes, Ketones and Carboxylic AcidsNumerical
The dipole moment of propanone is 2.88 D, where 1 D = 3.336 × 10⁻³⁰ C m…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
The dipole moment of propanone is , where . Suppose that all of it came from the C=O bond, with a length of . Find the dipole moment in coulomb metres, and the charge that would have to sit on each end, as a fraction of the elementary charge . What does the answer say about the bond?
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
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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.
Given. , .
Step 1. .
Step 2. We want , so .
Step 3. .
Answer: about on each end. The C=O bond is strongly polar, but it is not fully ionic.
Check. A fully ionic bond would give . This is only an upper estimate, because the other bonds of the molecule add a little to the dipole.
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