Identify the most acidic proton in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer. [Always start by drawing the conjugate base.]
(d)

검증된 단계별 안내

Step 1: Begin by drawing the conjugate base for each molecule. For the benzyl proton (H attached to the CH2 group next to the benzene ring), remove the proton to form a benzyl carbanion. For the hydroxyl proton (OH group), remove the proton to form an alkoxide ion.

Step 2: Analyze the stability of the conjugate bases. The benzyl carbanion benefits from resonance stabilization because the negative charge can delocalize into the aromatic ring. This resonance effect significantly increases the stability of the benzyl carbanion.

Step 3: Compare this to the alkoxide ion formed from the hydroxyl group. The alkoxide ion does not have resonance stabilization, but it does have inductive effects from the surrounding alkyl groups. However, these effects are weaker compared to resonance stabilization.

Step 4: Consider the electronegativity of the atoms involved. Oxygen in the hydroxyl group is more electronegative than carbon in the benzyl group, which means the alkoxide ion can better stabilize the negative charge compared to a simple carbanion. However, resonance stabilization in the benzyl carbanion outweighs this factor.

Step 5: Conclude that the benzyl proton is more acidic because its conjugate base (benzyl carbanion) is more stable due to resonance effects. Structural features like resonance stabilization are weighted heavily in determining acidity.

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주요 개념

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Acidity and pKa

Acidity in organic chemistry refers to the tendency of a compound to donate a proton (H+). The strength of an acid is often measured by its pKa value; lower pKa values indicate stronger acids. Understanding the relationship between acidity and pKa is crucial for identifying the most acidic proton in a given structure.

Conjugate Base Stability

The stability of the conjugate base formed after deprotonation is a key factor in determining acidity. A more stable conjugate base corresponds to a stronger acid. Factors influencing stability include resonance, electronegativity of atoms, and inductive effects, which can help predict which proton is more acidic.

Structural Features Influencing Acidity

Various structural features can affect the acidity of protons in organic molecules. These include the presence of electronegative atoms, resonance structures, and hybridization of the atom bearing the proton. Analyzing these features allows for a systematic approach to determine which proton is the most acidic in a pair.

Identify the most acidic proton in each pair. Tell which structural features you analyzed and why you weighted them as you did in picking one answer. [Always start by drawing the conjugate base.](d)