Textbook Question
Draw the condensed structural or line-angle formula for the alcohol produced when hydrogen and a nickel catalyst reduce each of the following:
a.
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15. Aldehydes and Ketones
Reduction of Aldehydes and Ketones
Problem 20a
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.
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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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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