Question

Which of the following item(s) explain the differences between the Ka values. Choose one or more: A. The negative charge is on the more electronegative fluorine atom in trifluoroacetate. B. The oxidation state for oxygen in trifluoroacetate is more negative than the oxidation state for oxygen in acetate. C. The trifluoroacetate molecule has more resonance structures than the acetate molecule. D. The electron-withdrawing fluorine atoms pull electron density from the oxygen in trifluoroacetate. The negative charge is more stabilized in trifluoroacetate by this effect.

Answer 1

Answer:

D. The electron-withdrawing fluorine atoms pull electron density from the oxygen in trifluoroacetate. The negative charge is more stabilized in trifluoroacetate by this effect.

Explanation:

The structures of trifluoroacetate and acetic acid are both shown in the image attached.

The trifluoroacetate anion (CF3CO2-), just like the acetate anion has in the middle, two oxygen atoms.

However, in the trifluoroacetate anion, there are also three electronegative fluorine atoms attached to the nearby carbon atom attached to the carbonyl, and these pull some electron density through the sigma bonding network away from the oxygen atoms, thereby spreading out the negative charge further. This effect, called the "inductive effect" stabilizes the anion formed,the trifouoroacetate anion is thus more stabilized than the acetate anion.

Hence, trifluoroacetic acid is a stronger acid than acetic acid, having a pKa of -0.18.