TAILIEUCHUNG - Lecture Organic chemistry - Chapter 7: Unimolecular substitution and elimination

Lecture Organic chemistry - Chapter 7: Unimolecular substitution and elimination. The main contents of this chapter include all of the following: Some observations, a new mechanism, what is the intermediate? The mechanism explains the data, the strong effect of polar solvents on the SN1 reaction,.and other contents. | Relative “rates” of the four arrows differ and depend on substrate, reagent, and conditions C H C L B Nu : - : - Chapter 7: Unimolecular Substitution And Elimination E1, E2 SN2, SN1, E1, E2 E1, E2 SN2, SN1 (CH3)2CH Br (CH3)3C Br H OCH3 + H OH (CH3)3C OCH3 H Br + Hydrolysis Generally: “Solvolysis” Some Observations Recall from Chapter 6: Indeed: Tertiary! H Br + (CH3)2CH OH + Methanolysis Secondary Lousy Nu Lousy Nu Moderate rate Fast! 8/9/2015 © Univesity of California 2 1. Rate = k [R-L], 1st order unimolecular, only R-L in rate-determining TS: “bottleneck”. 2. Stereochemistry: not stereospecific, . enantiomerically pure starting material leads to (extensively) racemic products; pure cis (or trans) gives cis/trans mixtures, etc Both observations inconsistent with SN2 mechanism A New Mechanism k1 Intermediate 3. Accelerates with polar (best with protic, in contrast to SN2) solvents: Hexane > CH3OH . . . . (CH3)3OCH3 . . (CH3)3CN3 wins 8/9/2015 © Univesity of California 4 What Is The Intermediate? Mechanism 1. Electron deficient! 2. 3. Unimolecular nucleophilic substitution: 1st Order rate law Racemization Acceleration in polar solvents Acceleration with better L Product determining step occurs after rate determining step SN1 SN1 The Mechanism Explains The Data SN1PotE Bottleneck: SN2 Versus SN1 “Bottleneck” Racemization In practice: Often, slight inversion is observed, due to “ion pairing”, R+····Br-. SN1Racem The Strong Effect Of Polar Solvents On The SN1 Reaction Increasing solvent polarity speeds reaction Increasing solvent polarity retards reaction As Expected: Good Leaving Groups Accelerate The SN1 Reaction The Nucleophile Has No Effect On The Rate Of The SN1 Reaction All reactions take place at the same rate k1. But in .

• Hoá học
• Organic chemistry
• Lecture Organic chemistry
• Hóa học hữu cơ
• Bài giảng Hóa học hữu cơ
• Unimolecular substitution
• In this workbook
• experiments are elaborated using small scale glassware and equipments from a Small Lab Kit
• developed at the Department of Chemistry
• Faculty of Science
• Chulalongkorn University in Thailand
• This Small Lab Kit was created as a result of the research project entitled “Chemistry Laboratory Based on Chemical Safety and Pollution Minimization” sponsored by Thai Research Fund (RDG 3 07 2543)
• One of the outcomes of this project is the organic laboratory book entitled “Organic Chemistry Laboratory Based on Chemical Safety and Pollution Minimization” written in Thai by professors from 7 universities in this project
• They compiled
• adjusted and tested the experiments taken from several traditional organic chemistry laboratory books using the prototype of Small Lab Kit
• Currently
• some selected experiments from this Thai organic chemistry laboratory text have further been modified
• rewritten and edited in English as appeared in this workbook
• Some experiments ar
• Ebook Organic chemistry
• Nucleophilic substitution
• Determining organic structures
• nucleophilic addition
• Organic structures
• Electrophilic aromatic substitution
• Principles of organic chemistry
• Methods of organic chemistry
• The methane series
• The acetylene series
• Polybasic acids
• High school
• University entrance exam
• Teaching organic chemistry
• Organic chemistry exam question
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• Advanced practical organic chemistry
• Functional groups
• Organic synthesis reagents
• The structure
• Reactions of organic names
• Fundamentals of organic chemistry
• Carbonyl alpha substitution reactions
• Condensation reactions
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• The structures of organic molecules
• Mass spectrometers
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• Strain and stability
• Covalent binding forces
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• Thermal pericyclic reactions
• The study of organic chemistry
• Stereochemistry and resonance
• Identification of organic compounds
• Elimination reactions
• Electrophilic addition reactions
• Electron delocalization
• Organic compounds
• Cyclic hydrocarbons
• Aromatic alcohols
• Aromatic compounds containing
• Inorganic chemistry
• A guidebook to mechanism in organic chemistry
• Aromatic systems
• Linear free energy relationships
• Symmetry controlled reactions
• Fatty acid catabolism
• The chemistry of the carbonyl group
• The industrial road toward increasing efficiency
• Chemistry of benzene
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• Summary of Organic Chemistry Dotoral Thesis
• Organic Chemistry Dotoral Thesis
• Natural Products Chemistry
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• Ideas in chemistry
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• Electronic Structure
• Electronic configurations of atoms
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• Chlorination of Methane
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