Textbook Question
We have studied a number of pericyclic reactions previously. Draw the mechanism of the steps shown. The section number where this material was first studied is given for your review.
(c)
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Ch. 22 - Conjugated Systems II: Pericyclic Reactions
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471
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Table of contents
- Ch. 2 - General Chemistry Translated: Finding the Electrons114
- Ch. 3 - Alkanes and Cycloalkanes: Properties and Conformational Analysis109
- Ch. 4 - Acids and Bases: Electron Flow144
- Ch. 5 - Chemical Reaction Analysis: Thermodynamics and Kinetics118
- Ch. 6 - Stereoisomerism: Arrangement of Atoms in Space112
- Ch. 7 - Principles of Green (Organic) Chemistry3
- Ch. 8 - Alkenes I: Properties and Electrophilic Additions158
- Ch. 9 - Alkenes II: Oxidation and Reduction150
- Ch. 10 - Alkynes: Electrophilic Addition and Redox Reactions101
- Ch. 11 - Properties and Synthesis of Alkyl Halides: Radical Reactions108
- Ch. 12 - Substitution and Elimination: Reactions of Haloalkanes172
- Ch. 13 - Alcohols, Ethers and Related Compounds: Substitution and Elimination239
- Ch. 14 - Structural Identification I: Infrared Spectroscopy and Mass Spectrometry54
- Ch. 15 - Structural Identification II: Nuclear Magnetic Resonance Spectroscopy93
- Ch. 16 - Metals in Organic Chemistry48
- Ch. 17 - Carbonyl Addition Reactions: Aldehydes and Ketones45
- Ch. 18 - Nucleophilic Acyl Substitution I: Carboxylic Acids18
- Ch. 19 - Nucleophilic Acyl Substitution II: Carboxylic Acid Derivatives39
- Ch. 20 - Enolates: Carbonyl Addition and Substitution13
- Ch. 21 - Conjugated Systems I: Stability and Addition Reactions56
- Ch. 22 - Conjugated Systems II: Pericyclic Reactions54
- Ch. 23 - Benzene I: Aromatic Stability and Substitution Reactions64
- Ch. 24 - Benzene II: Reactions Influenced by the Aromatic Ring62
- Ch. 25 - Amines: Structure, Reactions, and Synthesis27
- Ch. 26 - Amino Acids, Proteins, and Peptide Synthesis9
- Ch. 27 - Carbohydrates, Nucleic Acids, and Lipids54
Mullins1st EditionOrganic Chemistry: A Learner Centered ApproachISBN: 9780137566471Not the one you use?Change textbook
Chapter 21, Problem 5
The SN2 reaction is the concerted, backside displacement of a good leaving group by a nucleophile. Why do nucleophiles attack from the back in SN2 reactions?
Verified step by step guidance1
Understand the S_N2 reaction mechanism: The S_N2 reaction is a bimolecular nucleophilic substitution reaction where the nucleophile attacks the electrophilic carbon atom in a single, concerted step, displacing the leaving group.
Recognize the geometry of the substrate: The carbon atom undergoing substitution is sp³ hybridized, forming a tetrahedral geometry. The leaving group occupies one of the positions around the carbon atom.
Explain the steric hindrance at the front: The front side of the carbon atom is sterically hindered by the leaving group, making it difficult for the nucleophile to approach from this direction.
Discuss the electronic factors: The backside attack allows the nucleophile to approach the carbon atom opposite the leaving group, where the antibonding orbital (σ*) of the C-LG bond is accessible. This interaction weakens the C-LG bond, facilitating its cleavage.
Conclude with the stereochemical outcome: The backside attack in S_N2 reactions results in an inversion of configuration at the carbon center, often referred to as a 'Walden inversion,' which is a hallmark of this reaction mechanism.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
S_N2 Reaction Mechanism
The S_N2 reaction is a bimolecular nucleophilic substitution process where a nucleophile attacks an electrophile, leading to the simultaneous displacement of a leaving group. This mechanism is characterized by a single transition state and results in the inversion of configuration at the carbon center, which is crucial for understanding stereochemical outcomes.
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Heck Reaction Mechanism
Backside Attack
In S_N2 reactions, nucleophiles attack the electrophile from the opposite side of the leaving group, known as backside attack. This orientation minimizes steric hindrance and allows for effective overlap of the nucleophile's orbitals with the electrophile's, facilitating the formation of new bonds while breaking the old ones.
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02:16Using HX acids via SN2 reaction.
Leaving Group Ability
The ability of a leaving group to depart from the substrate is critical in S_N2 reactions. Good leaving groups, such as halides or sulfonates, stabilize the transition state and enhance the reaction rate. Understanding the nature of leaving groups helps predict the feasibility and speed of nucleophilic substitution reactions.
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03:06How to use the factors affecting acidity to predict leaving group ability.
Related Practice
Textbook Question
We have studied a number of pericyclic reactions previously. Draw the mechanism of the steps shown. The section number where this material was first studied is given for your review.
(a)
1036
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Textbook Question
Draw two important resonance structures involving the C―O π bond for the molecule shown. To which carbons would you expect a nucleophile to add?
1400
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Textbook Question
Draw the molecular orbital picture for (a) ethene. Label the HOMO and LUMO of each.
1872
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Textbook Question
We have studied a number of pericyclic reactions previously. Draw the mechanism of the steps shown. The section number where this material was first studied is given for your review.
(b)
726
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Textbook Question
What frequency of light would be required to excite an electron if the HOMO–LUMO energy gap was 33.9 kcal/mol (142 kJ/mol)?
1094
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