Textbook Question
Identify the stronger base in each pair. Explain your choice. Citing pKa values is not an acceptable answer.
(a)
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3. Acids and Bases
Ranking Acidity
4:20 minutesProblem 44c
Textbook Question
Without using pKa values, pick out the least reactive (most stable) base in each pair. Explain your answer.
(c) 
Verified step by step guidance1
Step 1: Understand the concept of base stability. A base's stability is influenced by factors such as resonance, electronegativity, inductive effects, and steric hindrance. The more stable a base, the less reactive it is.
Step 2: Examine resonance effects. If a base can delocalize its negative charge through resonance, it will be more stable. Compare the structures in the pair to see if one has resonance stabilization.
Step 3: Consider electronegativity. A base with its negative charge on a more electronegative atom will be more stable. Check the atoms bearing the negative charge in each base of the pair.
Step 4: Evaluate inductive effects. Electron-withdrawing groups near the negatively charged atom can stabilize the base by pulling electron density away. Look for such groups in the structures.
Step 5: Assess steric hindrance. A base with bulky groups around the negatively charged atom may be less stable due to steric repulsion. Compare the steric environments of the bases in the pair.
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Video duration:
4mKey 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 substance to donate protons (H⁺), while basicity is the ability to accept protons. The stability of a base is often inversely related to its reactivity; a more stable base is less likely to react with protons. Understanding the relationship between acids and bases is crucial for determining which base is less reactive in a given pair.
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Resonance Stabilization
Resonance stabilization occurs when a molecule can be represented by multiple valid Lewis structures, leading to a delocalization of electrons. This delocalization can enhance the stability of a base, making it less reactive. When comparing bases, those that can stabilize their negative charge through resonance are typically more stable and less reactive.
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Electronegativity and Charge Distribution
Electronegativity is the tendency of an atom to attract electrons towards itself. In the context of bases, the distribution of charge and the electronegativity of atoms can influence stability. A base with a negative charge on a more electronegative atom is generally more stable, as the electronegative atom can better accommodate the negative charge, leading to decreased reactivity.
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