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Chapter 16: Problem 11

Bisulfite addition is generally far less successful with ketones than it is with aldehydes. Explain why.

Short Answer

Expert verified
Bisulfite addition is less successful with ketones because they are less electrophilic and more sterically hindered compared to aldehydes.

Step by step solution

01

Understand the Differences between Aldehydes and Ketones

Identify that aldehydes have at least one hydrogen attached to the carbonyl carbon, whereas ketones have two alkyl groups attached to the carbonyl carbon.
02

Consider the Electronic Effects

Recognize that ketones are less electrophilic than aldehydes due to the electron-donating effects of the two alkyl groups attached to the carbonyl carbon. This makes ketones less reactive.
03

Steric Effects

Understand that steric hindrance is greater in ketones since they have two alkyl groups which can hinder the approach of nucleophiles such as bisulfite.
04

Analyze Bisulfite Addition Mechanism

Bisulfite adds to the carbonyl group by nucleophilic attack. Aldehydes are more susceptible to nucleophilic attack because they are less sterically hindered and more electrophilic.
05

Conclude the Reason for the Difference

Conclude that the combination of lower electrophilicity and increased steric hindrance in ketones compared to aldehydes makes bisulfite addition less successful with ketones.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

ketone reactivity
Ketones possess a carbonyl group that is bonded to two alkyl groups. These alkyl groups donate electrons through inductive effects. This electron-donating effect reduces the partial positive charge on the carbonyl carbon, making it less electrophilic. As a result, ketones are generally less reactive towards nucleophiles compared to aldehydes, which only have one alkyl group or a hydrogen atom attached to the carbonyl carbon.
aldehyde reactivity
Aldehydes have one carbonyl carbon attached to at least one hydrogen atom and potentially one alkyl group. The presence of a hydrogen atom, which does not donate electron density, makes the carbonyl carbon more electrophilic. This increased electrophilicity makes aldehydes more reactive towards nucleophilic addition reactions, such as bisulfite addition, when compared to ketones.
nucleophilic attack
In organic chemistry, nucleophilic attack is the process where a nucleophile donates an electron pair to an electrophile to form a new chemical bond. For the bisulfite addition reaction, the bisulfite ion (HSO3-) acts as the nucleophile, attacking the carbonyl carbon of the aldehyde or ketone. Since aldehydes are more electrophilic, they are more readily attacked by nucleophiles like bisulfite, making the addition reaction more successful.
steric hindrance
Steric hindrance refers to the repulsion between bulky groups in a molecule that can hinder chemical reactions. In ketones, the presence of two alkyl groups around the carbonyl carbon creates more steric hindrance. This makes it difficult for nucleophiles like bisulfite to approach the carbonyl carbon. In contrast, aldehydes have either one alkyl group or no alkyl groups, resulting in less steric hindrance and easier access for nucleophiles.
electrophilicity in organic chemistry
Electrophilicity describes the capability of a molecule or atom to act as an electron-pair acceptor in a chemical reaction. It is a key factor in determining how reactive a carbonyl compound is towards nucleophilic attack. Aldehydes, with their higher electrophilicity, are more favorable targets for nucleophiles compared to ketones. This is because the carbonyl carbon in aldehydes has a higher partial positive charge, making it more attractive to electron-rich species like nucleophiles.

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Most popular questions from this chapter

Draw structures for the following compounds: (a) \(p\)-nitrobenzaldehyde (b) \((S)-4\)-methylhexanal (c) \((E)-2\)-butenal (d) \(c i s-2-\) bromocyclopropanecarboxaldehyde

Draw structures for the following compounds: (a) 3,5 -di-tert-butyl-4-hydroxybenzaldehyde (b) \((S)-5\)-bromo-2-cyclopentenone (c) \(2,4^{\prime}\)-dichloro-4-nitrobenzophenone (d) 6-methyl-2-pyridinecarboxaldehyde (e) (E)-4-phenyl-3-buten-2-one (f) aminoacetaldehyde dimethyl acetal

Draw the structures for: (a) 2,3-dichlorohexanal; (b) 4-hydroxybutanal;(c) 2 -bromo-3-pentanone; (d) 3 -methyl-2-butanone.

Explain why hemiacetals, but not full acetals, are formed under basic conditions.

Draw structures for the following compounds: (a) methyl propyl ketone (b) 2-pentanone (c) 2,3 -hexanedione (d) butyrophenone (e) 3-bromo-4-chloro-5-iodo-2-octanone
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