Textbook Question
Compare the properties of propan-2-ol (I) and the hexafluoro analog (II).
(a) Compound II has almost triple the molecular weight of I, but II has a lower boiling point. Explain.
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3. Acids and Bases
Ranking Acidity
Multiple Choice
Which of the following carboxylic acids is the most acidic?
A
Acetic acid ()
B
Trifluoroacetic acid ()
C
Propanoic acid ()
D
Benzoic acid ()
Verified step by step guidance1
Identify the key factor that influences acidity in carboxylic acids: the stability of the conjugate base formed after deprotonation of the acid (loss of H\(\textsuperscript{+}\) from the \( -COOH \) group).
Recognize that electron-withdrawing groups attached to the carbon adjacent to the carboxyl group increase acidity by stabilizing the negative charge on the conjugate base through inductive effects.
Analyze each acid: Acetic acid has a methyl group (electron-donating), Propanoic acid has an ethyl group (also electron-donating), Benzoic acid has a phenyl group (which can have resonance effects but is less electron-withdrawing than fluorine), and Trifluoroacetic acid has three fluorine atoms (strongly electron-withdrawing) attached to the alpha carbon.
Conclude that trifluoroacetic acid's three fluorine atoms strongly stabilize the conjugate base via the inductive effect, making it the most acidic among the given options.
Summarize that acidity order is determined by the ability of substituents to stabilize the conjugate base, with electron-withdrawing groups increasing acidity and electron-donating groups decreasing it.
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