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3. Which is a stronger base, and why? I-Z: H N

3. Which is a stronger base, and why? I-Z: H N

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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**Question 3:** Which is a stronger base, and why? **Description of diagrams:** - The first structure is a piperidine molecule. It is a six-membered ring with five carbon atoms and one nitrogen atom. The nitrogen atom has a hydrogen attached, and there is a lone pair of electrons on the nitrogen. - The second structure is a pyridine molecule. It is also a six-membered ring with five carbon atoms and one nitrogen atom. The nitrogen atom has a lone pair of electrons but no hydrogen attached. **Explanation:** In comparing the basicity of the two compounds, the strength of a base is generally related to the availability of the lone pair of electrons on the nitrogen atom to accept protons. Piperidine is typically a stronger base than pyridine. This is because the lone pair of electrons on the nitrogen in piperidine is more available for protonation, as pyridine's lone pair is part of an aromatic system, making it less available for bonding with a proton.
Transcribed Image Text:**Question 3:** Which is a stronger base, and why? **Description of diagrams:** - The first structure is a piperidine molecule. It is a six-membered ring with five carbon atoms and one nitrogen atom. The nitrogen atom has a hydrogen attached, and there is a lone pair of electrons on the nitrogen. - The second structure is a pyridine molecule. It is also a six-membered ring with five carbon atoms and one nitrogen atom. The nitrogen atom has a lone pair of electrons but no hydrogen attached. **Explanation:** In comparing the basicity of the two compounds, the strength of a base is generally related to the availability of the lone pair of electrons on the nitrogen atom to accept protons. Piperidine is typically a stronger base than pyridine. This is because the lone pair of electrons on the nitrogen in piperidine is more available for protonation, as pyridine's lone pair is part of an aromatic system, making it less available for bonding with a proton.
**Question 4:** Explain why the pKa values of the indicated hydrogen atoms change as they do for these three compounds. **Description of the Diagram:** The diagram presents three chemical structures, each with an indicated hydrogen atom and an associated pKa value. 1. **First Structure:** - A hydrocarbon chain with a single hydrogen atom highlighted. - The pKa value is given as 50. 2. **Second Structure:** - A carbon skeleton with a carbonyl group (C=O) attached, next to which a hydrogen atom is highlighted. - The pKa value is indicated as 20. 3. **Third Structure:** - A similar structure to the second, but with two carbonyl groups (C=O) on either side of the central carbon with the highlighted hydrogen atom. - The pKa value is noted as 10. **Explanation:** The pKa values decrease (from 50 to 10) as the graph progresses from the first to the third compound. This change occurs due to the increasing stabilization of the conjugate base by resonance and the electronegative nature of the oxygen in the carbonyl group. As more carbonyl groups are present, such as in the third compound, the hydrogen becomes more acidic, leading to a lower pKa value.
Transcribed Image Text:**Question 4:** Explain why the pKa values of the indicated hydrogen atoms change as they do for these three compounds. **Description of the Diagram:** The diagram presents three chemical structures, each with an indicated hydrogen atom and an associated pKa value. 1. **First Structure:** - A hydrocarbon chain with a single hydrogen atom highlighted. - The pKa value is given as 50. 2. **Second Structure:** - A carbon skeleton with a carbonyl group (C=O) attached, next to which a hydrogen atom is highlighted. - The pKa value is indicated as 20. 3. **Third Structure:** - A similar structure to the second, but with two carbonyl groups (C=O) on either side of the central carbon with the highlighted hydrogen atom. - The pKa value is noted as 10. **Explanation:** The pKa values decrease (from 50 to 10) as the graph progresses from the first to the third compound. This change occurs due to the increasing stabilization of the conjugate base by resonance and the electronegative nature of the oxygen in the carbonyl group. As more carbonyl groups are present, such as in the third compound, the hydrogen becomes more acidic, leading to a lower pKa value.
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