Textbook Question
Rank the amines in each set in order of increasing basicity.
(c)
20. Phenols
Phenol Acidity
Multiple Choice
Rank the following molecules in increasing order of acidity (least acidic to most acidic).
A
I < IV < II < III
B
I < III < IV < II
C
V < II < III < I
D
III < II < IV < I
Verified step by step guidance1
Identify the functional groups attached to the benzene ring in each molecule. Molecule I has a nitro group (NO2) at the para position, Molecule II has a hydroxyl group (OH), Molecule III has both a nitro group (NO2) at the ortho position and a hydroxyl group (OH), and Molecule IV has a tert-butyl group and a hydroxyl group (OH).
Understand the effect of substituents on acidity. The nitro group is an electron-withdrawing group, which increases acidity by stabilizing the negative charge on the conjugate base. The tert-butyl group is an electron-donating group, which decreases acidity.
Consider the position of the nitro group in Molecule III. The ortho position allows for stronger electron-withdrawing effects due to proximity, enhancing the acidity compared to the para position in Molecule I.
Compare the acidity of Molecule II and Molecule IV. Molecule II has only a hydroxyl group, while Molecule IV has a tert-butyl group that decreases acidity. Therefore, Molecule II is more acidic than Molecule IV.
Rank the molecules based on the analysis: Molecule IV is the least acidic due to the electron-donating tert-butyl group, followed by Molecule II with only a hydroxyl group, then Molecule I with a para nitro group, and Molecule III is the most acidic due to the ortho nitro group.
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