CHEM 3332 1st Edition Lecture 8Outline of Last Lecture Reactions of Ethers-ethers are unreactive to many organic reagents-ether bond (C-O) is stable to strong Nu/strong base oxidation reactionsI. Cleavage by strong acids HI and HBR, not HCLMechanismII. Autoxidation (DANGER!!!): peroxidesSynthesis of EpoxidesI. Epoxidation of alkanes with peroxyacidsMechanism: a concerted processElectron rich pi bonds react fastesStereochemistry of alkene is maintainedII. Intramolecular WilliamsonLarger cyclic ethers can also be formed:Reaction o EpoxidesI. Acid – catalyzed cleavageII. Base – catalyzed cleavageIf the epoxide is symmetrical, the results of acid cat. and base cat.are the same. Consider each process with asymmetrical apoxides:I. Acid – catalyzed cleavageII. Base – catalyzed cleavageSummary1. Weak nucleophiles (H2O, ROH, Cl-) only react with protonated epoxides in acidic conditions2. Strong nucleophile (CH-, RO-, NH2-, CN-, carbanions) react with unprotinated epoxide3. Acid- cat. process Nu attacks the more substituted carbon4. Base cat. process Nu attacks the less substituted carbon.III. Reaction of Epoxide with Gringard/Organolithium ReagentsIV. Reaction of Epoxide with Acetylide IonCompare to: Outline of Current Lecture Chapter 15: Conjugated Systems, Orbital Symmetry, UV SpectroscopyTypes of Dienes:Nomenclature: review alkenes – diene (cis/trans/EZ)Preparation of compound diene: elimination of HX from allylic halideStability of Conjugated Dienes is slightly more stable1.2.These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.3.4.Explanation of Stability:AllylCation:C+ Stability:How does conjugation affect reactivity?Mechanism of addition of HBRRatio of products: At Low temperature: less stable alkeneAt High temperature: more stable alkeneThe process above is an example of Rate (Kinetic) versus Equilibriu, (Thermodynamic) Control. Chart:Chart:Current
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