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Which is more acidic? Explain your reasoning H3C. OH ČH3 2-methylpropanoic acid ethanoic acid

Which is more acidic? Explain your reasoning H3C. OH ČH3 2-methylpropanoic acid ethanoic acid

Chemistry
Chemistry
10th Edition
ISBN:9781305957404
Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Publisher:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
Chapter1: Chemical Foundations
Section: Chapter Questions
Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...
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### Which is more acidic? Explain your reasoning #### Molecular Structures: 1. **2-methylpropanoic acid** (left) - Structural Formula: - Contains a carboxyl group (—COOH) attached to a carbon chain with a branching methyl group. - The structural formula is: H₃C-CH(CH₃)-COOH 2. **Ethanoic acid** (right) - Structural Formula: - Consists of a simpler carboxyl group (—COOH) directly bonded to a methyl group (CH₃). - The structural formula is: CH₃-COOH #### Acidity Comparison Explanation: - **Stability of Conjugate Base**: The acidity of an acid is often related to the stability of its conjugate base. When an acid loses a hydrogen ion (H⁺), it forms its conjugate base. A more stable conjugate base means a more acidic parent acid. - **Ethanoic Acid**: - The conjugate base of ethanoic acid (acetate ion, CH₃COO⁻) is stabilized by resonance. The negative charge can be delocalized between the two oxygen atoms, which spreads out and stabilizes the charge. - **2-methylpropanoic Acid**: - The conjugate base of 2-methylpropanoic acid (isobutyrate ion, CH₃(CH₃)CHCOO⁻) lacks significant resonance stabilization. The presence of the additional methyl group donates electron density, which slightly destabilizes the negative charge on the conjugate base. - **Inductive Effects**: Electron-donating groups (like a methyl group) decrease acidity because they increase electron density on the conjugate base, making it less stable. - **Ethanoic Acid**: Has no extra electron-donating groups other than the methyl group attached directly to the carboxyl carbon. - **2-methylpropanoic Acid**: Has an additional methyl group attached to the alpha carbon. This increases electron density by an inductive effect, making the conjugate base less stable and thus making 2-methylpropanoic acid less acidic. In conclusion, **ethanoic acid (acetic acid)** is more acidic than **2-methylpropanoic acid (isobutyric acid)** because its conjug
Transcribed Image Text:### Which is more acidic? Explain your reasoning #### Molecular Structures: 1. **2-methylpropanoic acid** (left) - Structural Formula: - Contains a carboxyl group (—COOH) attached to a carbon chain with a branching methyl group. - The structural formula is: H₃C-CH(CH₃)-COOH 2. **Ethanoic acid** (right) - Structural Formula: - Consists of a simpler carboxyl group (—COOH) directly bonded to a methyl group (CH₃). - The structural formula is: CH₃-COOH #### Acidity Comparison Explanation: - **Stability of Conjugate Base**: The acidity of an acid is often related to the stability of its conjugate base. When an acid loses a hydrogen ion (H⁺), it forms its conjugate base. A more stable conjugate base means a more acidic parent acid. - **Ethanoic Acid**: - The conjugate base of ethanoic acid (acetate ion, CH₃COO⁻) is stabilized by resonance. The negative charge can be delocalized between the two oxygen atoms, which spreads out and stabilizes the charge. - **2-methylpropanoic Acid**: - The conjugate base of 2-methylpropanoic acid (isobutyrate ion, CH₃(CH₃)CHCOO⁻) lacks significant resonance stabilization. The presence of the additional methyl group donates electron density, which slightly destabilizes the negative charge on the conjugate base. - **Inductive Effects**: Electron-donating groups (like a methyl group) decrease acidity because they increase electron density on the conjugate base, making it less stable. - **Ethanoic Acid**: Has no extra electron-donating groups other than the methyl group attached directly to the carboxyl carbon. - **2-methylpropanoic Acid**: Has an additional methyl group attached to the alpha carbon. This increases electron density by an inductive effect, making the conjugate base less stable and thus making 2-methylpropanoic acid less acidic. In conclusion, **ethanoic acid (acetic acid)** is more acidic than **2-methylpropanoic acid (isobutyric acid)** because its conjug
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