Textbook Question
Four pairs of compounds are shown. In each pair, one of the compounds reacts more quickly, or with a more favorable equilibrium constant, than the less conjugated system. In each case, explain the enhanced reactivity.
(d)
3. Acids and Bases
Ranking Acidity
3:02 minutesProblem 63c
Textbook Question
Identify the stronger base in each pair. Explain your choice. Citing pKa values is not an acceptable answer.
(c) 
Verified step by step guidance1
Step 1: Understand the concept of basicity. A base is a substance that can accept a proton (H⁺). The strength of a base depends on its ability to stabilize the negative charge after accepting a proton. Factors such as electronegativity, resonance, and steric hindrance play a role in determining basicity.
Step 2: Analyze the molecular structure of each compound in the pair. Look for features such as the presence of electronegative atoms, resonance stabilization, or bulky groups that might affect the ability of the molecule to accept and stabilize a proton.
Step 3: Consider the role of resonance. If one of the bases has resonance structures that can delocalize the negative charge after accepting a proton, it will generally be a weaker base because the negative charge is more stabilized.
Step 4: Evaluate the electronegativity of the atoms involved. A base with a less electronegative atom holding the negative charge will generally be stronger because it is less able to stabilize the charge, making it more reactive.
Step 5: Assess steric hindrance. If one of the bases has bulky groups near the site where it would accept a proton, this can make it less accessible to the proton and therefore a weaker base.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Acidity and Basicity
Acidity refers to the tendency of a compound to donate protons (H⁺ ions), while basicity is the tendency to accept protons. The strength of a base is often related to its ability to stabilize the positive charge that results from protonation. Understanding the relationship between acids and bases is crucial for determining which compound in a pair is the stronger base.
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Resonance Stabilization
Resonance stabilization occurs when a molecule can be represented by multiple valid Lewis structures, allowing for the delocalization of electrons. A base that can stabilize its negative charge through resonance is generally stronger because it can distribute the charge over a larger area, making it less likely to re-protonate. This concept is essential for comparing the basicity of different compounds.
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Electronegativity
Electronegativity is the tendency of an atom to attract electrons towards itself. In the context of basicity, a less electronegative atom is more likely to donate its electrons, making it a stronger base. Understanding the electronegativity of atoms within the compounds being compared helps in predicting which will be the stronger base in a given pair.
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