Textbook Question
Draw the structures of the hemiacetals or hemiketals formed in these reactions:
b.
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Ch.15 Aldehydes and Ketones
McMurry8th EditionFundamentals of GOBISBN: 9780134015187
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Table of contents
- Ch.1 Matter and Measurements27
- Ch.2 Atoms and the Periodic Table20
- Ch.3 Ionic Compounds8
- Ch.4 Molecular Compounds23
- Ch.5 Classification & Balancing of Chemical Reactions12
- Ch.6 Chemical Reactions: Mole and Mass Relationships28
- Ch.7 Chemical Reactions: Energy, Rate and Equilibrium64
- Ch.8 Gases, Liquids and Solids24
- Ch.9 Solutions52
- Ch.10 Acids and Bases25
- Ch.11 Nuclear Chemistry22
- Ch.12 Introduction to Organic Chemistry: Alkanes57
- Ch.13 Alkenes, Alkynes, and Aromatic Compounds47
- Ch.14 Some Compounds with Oxygen, Sulfur, or a Halogen50
- Ch.15 Aldehydes and Ketones45
- Ch.16 Amines42
- Ch.17 Carboxylic Acids and Their Derivatives57
- Ch.18 Amino Acids and Proteins82
- Ch.19 Enzymes and Vitamins63
- Ch.20 Carbohydrates44
- Ch.21 The Generation of Biochemical Energy65
- Ch.22 Carbohydrate Metabolism45
- Ch.23 Lipids42
- Ch.24 Lipid Metabolism33
- Ch.25 Protein and Amino Acid Metabolism24
- Ch.26 Nucleic Acids and Protein Synthesis45
Chapter 15, Problem 20a
The carbonyl group can be reduced by addition of a hydride ion (H–) and (H+) a proton. Removal of H– and H+ from an alcohol results in a carbonyl group.
a. To which atom of the carbonyl is the hydride ion added and why?
Verified step by step guidance1
The carbonyl group consists of a carbon atom double-bonded to an oxygen atom (C=O). This bond is polar because oxygen is more electronegative than carbon, creating a partial negative charge (δ⁻) on the oxygen and a partial positive charge (δ⁺) on the carbon.
The hydride ion (H⁻) is a nucleophile, meaning it is electron-rich and seeks out electron-deficient regions. In the carbonyl group, the carbon atom is electron-deficient due to the partial positive charge (δ⁺), making it the site where the hydride ion will attack.
When the hydride ion (H⁻) adds to the carbon atom of the carbonyl group, it forms a single bond with the carbon, breaking the double bond between carbon and oxygen. This results in the formation of an alkoxide ion (R-CH-O⁻).
The addition of a proton (H⁺) to the alkoxide ion neutralizes the negative charge on the oxygen, resulting in the formation of an alcohol (R-CH-OH).
In summary, the hydride ion is added to the carbon atom of the carbonyl group because the carbon is electron-deficient (δ⁺), making it susceptible to nucleophilic attack by the electron-rich hydride ion.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Carbonyl Group
The carbonyl group is a functional group characterized by a carbon atom double-bonded to an oxygen atom (C=O). It is a key feature in various organic compounds, including aldehydes and ketones. Understanding the structure and reactivity of the carbonyl group is essential for grasping how it interacts with nucleophiles, such as hydride ions, during reduction reactions.
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Functional Groups with Carbonyls Example 3
Hydride Ion (H⁻)
A hydride ion is a negatively charged ion (anion) consisting of one hydrogen atom with an extra electron. In organic chemistry, hydride ions act as strong nucleophiles, meaning they can donate electrons to electrophilic centers, such as the carbon atom in a carbonyl group. This donation leads to the reduction of the carbonyl compound, converting it into an alcohol.
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Reduction Reaction
Reduction is a chemical reaction that involves the gain of electrons or the decrease in oxidation state by a molecule, atom, or ion. In the context of carbonyl compounds, reduction typically involves the addition of hydrogen (from hydride ions) to the carbonyl carbon, transforming it into an alcohol. Understanding reduction is crucial for predicting the outcomes of reactions involving carbonyl groups.
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Related Practice
Textbook Question
For each compound shown next, determine whether it is a hemiacetal, a hemiketal, an acetal, or a ketal.
a.
b.
c.
d.
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Textbook Question
The carbonyl group can be reduced by addition of a hydride ion (H–) and (H+) a proton. Removal of H– and H+ from an alcohol results in a carbonyl group.
b. In the reaction, indicate which direction represents reduction and which represents oxidation.
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Textbook Question
A fundamental difference between aldehydes and ketones is that one can be oxidized to carboxylic acids but the other cannot. Which is which? Give an example of a test to differentiate aldehydes from ketones.
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Textbook Question
Glucose is the major sugar in mammalian blood. We often see it represented as either the "free aldehyde" or the cyclic hemiacetal forms shown here. Of the two forms of glucose, the cyclic hemiacetal is the preferred form found in blood. Can you suggest two reasons why?
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