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Ch. 2 - Acids and Bases: Central to Understanding Organic Chemistry
Bruice - Organic Chemistry 8th Edition
Bruice8th EditionOrganic ChemistryISBN: 9780135213711Not the one you use?Change textbook
All textbooksBruice 8th EditionCh. 2 - Acids and Bases: Central to Understanding Organic ChemistryProblem 34c,d
Chapter 3, Problem 34c,d

For each of the following compounds, indicate the atom that is protonated when an acid is added to a solution of the compound.
c. Chemical structure showing a compound with an oxygen atom, indicating the site of protonation when an acid is added.
d. Chemical structure showing a hexagonal ring with an amine group and an oxygen atom, indicating protonation sites.

Verified step by step guidance
1
Step 1: Analyze the structure of compound A. It contains a carbonyl group (C=O) and an ether oxygen atom. The ether oxygen has lone pairs of electrons, making it a likely site for protonation when an acid is added.
Step 2: Consider the structure of compound B. It contains a carbonyl group (C=O) and an amine group (-NH). The nitrogen atom in the amine group has lone pairs of electrons, making it a likely site for protonation when an acid is added.
Step 3: Recall that protonation occurs at the atom with the highest electron density or lone pairs that can interact with the proton (H⁺). In compound A, the ether oxygen is the most likely site for protonation due to its lone pairs.
Step 4: In compound B, the nitrogen atom in the amine group is the most likely site for protonation because nitrogen is more basic than oxygen and readily accepts a proton.
Step 5: Summarize the findings: For compound A, the ether oxygen is protonated. For compound B, the nitrogen in the amine group is protonated.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Protonation

Protonation is the addition of a proton (H⁺) to a molecule, which can significantly alter its chemical properties. In organic chemistry, this process often occurs in the presence of acids, where the proton attaches to a site on the molecule that has a lone pair of electrons, typically resulting in a positively charged species. Understanding which atom is protonated helps predict the behavior of the compound in reactions.
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Acid-Base Chemistry

Acid-base chemistry involves the transfer of protons between species, where acids donate protons and bases accept them. This concept is fundamental in organic reactions, as the nature of the acid and the basicity of the functional groups in the compounds dictate the site of protonation. Recognizing the acidic and basic sites in a molecule is crucial for predicting the outcome of acid-base reactions.
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The Lewis definition of acids and bases.

Functional Groups

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. In the context of the provided compounds, identifying functional groups such as alcohols, amines, or carbonyls is essential, as they influence the site of protonation. Each functional group has distinct properties that determine its reactivity in acid-base chemistry.
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Related Practice
Textbook Question

Fosamax (shown on the previous page) has six acidic groups. The active form of the drug, which has lost two of its acidic protons, is shown in the box. 

(Notice that the phosphorus atom in Fosamax and the sulfur atom in [Problem 36] can be surrounded by more than eight electrons because P and S are below the second row of the periodic table.)

a. Why are the OH groups bonded to phosphorus the strongest acids of the six groups?

b. Which of the remaining four groups is the weakest acid?

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Textbook Question

Using the table of pKa values given in [Appendix I] , answer the following:

d. Which is more electronegative: an sp3 oxygen or an sp2 oxygen?

e. Which compounds demonstrate that the relative electronegativities of a hybridized nitrogen atom are sp > sp2 > sp3?

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Textbook Question

For each of the following compounds, indicate the atom that is protonated when an acid is added to a solution of the compound.

a.

b.

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Textbook Question

Using the table of pKa values given in [Appendix I], answer the following:

a. Which is the most acidic organic compound in the table?

b. Which is the least acidic organic compound in the table?

c. Which is the most acidic carboxylic acid in the table?

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Textbook Question

Which is a stronger base?

a.

b.

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Textbook Question

If HCl is a weaker acid than HBr, why is ClCH2COOH a stronger acid than BrCH2COOH?

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