Question

Question #99dda

Answer 1

B. The carbonyl group of propanone is most polar.

Explanation:

The polarity of a carbonyl group is enhanced by hyperconjugation of the carbonyl π system with the `"C-H"` σ bonds on adjacent carbon atoms.

Propanone has six adjacent `"C-H"` σ bonds.
Pentan-3-one has four adjacent `"C-H"` σ bonds.
Ethanal has three adjacent `"C-H"` σ bonds.
Methanal has no adjacent `"C-H"` σ bonds.

This mirrors the observed order of dipole moments.

`"Propanone > pentan-2-one > ethanal > methanal"`
`color(white)(ml)"2.88 D" color(white)(ll)> color(white)(mll)"2.82 D" color(white)(ml)> color(white)(l)"2.75 D" > color(white)(m)"2.33 D"`