Textbook Question
For each indicated proton, suggest an approximate pKa value from Table 4.5. Rationalize your choice.
(d)
3. Acids and Bases
pKa
4:25 minutesProblem 29c,d
Textbook Question
Arrange each group of compounds in order of increasing basicity.
c. sodium benzoate, sodium ethoxide, and sodium phenoxide
d. pyridine, sodium ethoxide, and sodium acetate
Verified step by step guidance1
Step 1: Understand the concept of basicity. Basicity refers to the ability of a compound to accept protons (H⁺ ions). Strong bases are more effective at accepting protons.
Step 2: Analyze the structure of each compound in group (c). Sodium benzoate is the sodium salt of benzoic acid, sodium ethoxide is the sodium salt of ethanol, and sodium phenoxide is the sodium salt of phenol.
Step 3: Consider the electron-withdrawing or electron-donating effects of substituents in each compound in group (c). Sodium benzoate has an aromatic ring which can stabilize the negative charge, making it less basic. Sodium ethoxide is a strong base due to the alkoxide ion, and sodium phenoxide is less basic than sodium ethoxide due to resonance stabilization in the phenoxide ion.
Step 4: Analyze the structure of each compound in group (d). Pyridine is a nitrogen-containing aromatic compound, sodium ethoxide is an alkoxide ion, and sodium acetate is the sodium salt of acetic acid.
Step 5: Consider the basicity of each compound in group (d). Pyridine is a weak base due to resonance stabilization, sodium ethoxide is a strong base, and sodium acetate is less basic than sodium ethoxide due to resonance stabilization in the acetate ion.
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Video duration:
4mKey Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Basicity in Organic Compounds
Basicity refers to the ability of a compound to accept protons (H+ ions). In organic chemistry, the basicity of a compound is influenced by the availability of lone pairs on atoms like nitrogen or oxygen, and the stability of the resulting conjugate acid. Factors such as resonance, inductive effects, and hybridization play crucial roles in determining basicity.
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Resonance Stabilization
Resonance stabilization occurs when a compound can delocalize electrons across multiple atoms, reducing the availability of lone pairs for protonation and thus decreasing basicity. For example, sodium benzoate and sodium phenoxide have resonance structures that stabilize the negative charge, making them less basic compared to sodium ethoxide, which lacks such resonance.
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Inductive and Electron-Withdrawing Effects
Inductive effects involve the transmission of charge through a chain of atoms, affecting basicity. Electron-withdrawing groups, like the carbonyl group in sodium acetate, decrease basicity by pulling electron density away from the atom that would accept a proton. Conversely, electron-donating groups increase basicity by enhancing electron density on the proton-accepting atom.
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