Textbook Question
Reduction of an alkyne using the Lindlar catalyst, a reaction presented in Section 10.6.2, produces only the cis-alkene. Why?
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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 7c
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) 
Verified step by step guidance1
Step 1: Identify the type of pericyclic reaction involved. Based on the reactants and products, this appears to be a hydroboration reaction, which is a type of concerted addition reaction where boron adds to the less substituted carbon of an alkene.
Step 2: Analyze the reactants. The alkene (CH2=CH-CH2CH3) is the electron-rich species, and the borane (BH3) is the electron-deficient species. The reaction proceeds via a cyclic transition state.
Step 3: Draw the mechanism. In the hydroboration step, the π-electrons of the alkene interact with the empty p-orbital of boron, while one of the B-H bonds simultaneously donates a proton to the more substituted carbon. This results in syn addition of boron and hydrogen across the double bond.
Step 4: Show the product formation. The boron atom attaches to the less substituted carbon (CH2 group), and the hydrogen attaches to the more substituted carbon (CH group). This regioselectivity is due to steric and electronic factors.
Step 5: Review the stereochemistry. The addition of boron and hydrogen occurs in a syn fashion, meaning both groups are added to the same face of the alkene. This stereochemical outcome is consistent with the concerted nature of the reaction.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Pericyclic Reactions
Pericyclic reactions are a class of organic reactions that occur through a concerted mechanism, involving a cyclic transition state. These reactions often involve the rearrangement of electrons in a way that conserves orbital symmetry, allowing for the formation of new bonds without the need for intermediates. Common types include cycloadditions, electrocyclic reactions, and sigmatropic rearrangements.
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Properties and Types of Pericyclic Reactions
Hydroboration
Hydroboration is a chemical reaction that involves the addition of borane (BH3) to alkenes, resulting in the formation of organoboranes. This reaction proceeds via a concerted mechanism, where the boron atom adds to the less substituted carbon of the alkene, leading to syn-addition. Hydroboration is often followed by oxidation to yield alcohols, making it a valuable method for synthesizing alcohols from alkenes.
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Mechanism of Reactions
The mechanism of a chemical reaction describes the step-by-step process by which reactants are converted into products. It includes details about bond breaking and forming, the movement of electrons, and the role of intermediates. Understanding the mechanism is crucial for predicting the outcome of reactions, optimizing conditions, and designing new synthetic pathways in organic chemistry.
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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)
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Textbook Question
Diene A participates in a fast and efficient Diels–Alder reaction with maleic anhydride, the powerful dienophile from Assessment 22.9. However, the related diene B does not undergo a Diels–Alder reaction. Why?
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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)
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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.
(d)
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Textbook Question
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?
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