The acidities of certain organic molecules can change when the solvent is switched…
CHEMISTRY · Multi-part · A Level · Chemistry · Acids and bases · Acids and bases
Problem
The acidities of certain organic molecules can change when the solvent is switched from liquid water to an aprotic solvent such as dimethyl sulfoxide (DMSO).
Table 1 lists experimental pKa values measured in water at 25∘C.
Table 1 Acid strength in water
Molecule
pKa (water)
CH3COOH
4.76
C6H5OH
10.0
CF3CH2OH
12.4
Answer the following.
(a) Predict qualitatively ("increases," "decreases," or "remains approximately the same") how the acid strength of each molecule will change when the solvent is changed from water to DMSO. Justify each prediction.
(b) For one molecule of your choice from Table 1, explain in detail why the change in solvent affects its position of the acid–base equilibrium. Your discussion should reference specific intermolecular interactions between solvent molecules and both the acid and its conjugate base.
(c) Suppose an equimolar mixture of the three acids is dissolved in DMSO. Which acid will donate a proton most readily under these conditions? Support your answer with reasoning that integrates your predictions from part (a).