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CONCEPT: THE E2 MECHANISM A strong nucleophile reacts with an inaccessible leaving group to produce beta-elimination in one-step. E2 Properties (Circle One) Nucleophile = Strong / Weak Leaving Group = Unsubstituted / Highly Substituted Reaction coordinate = Transition State / Intermediate Reaction = Concerted / Two-Step Rate = Unimolecular / Bimolecular Rate = k[rx] / k[nu][rx] Stereochemistry = EXAMPLE: Rank the following alkyl halides in order of reactivity toward an E2 reaction. Page 2
CONCEPT: RECOGNIZING DIFFERENT β-hydrogens Elimination reactions remove β-hydrogens to create double bonds. The number of non-equivalent β-carbons with at least one determines the number of possible products. EXAMPLE: Identify the number of unique products that could be obtained through elimination. a. b. c. d. Page 3
CONCEPT: THE ANTI-COPLANAR REQUIREMENT E2 reactions require an anti-coplanar arrangement in order for the orbitals to overlap and create a new pi bond. When this occurs on cyclohexane, the leaving group and beta-proton must be DIAXIAL to each other. EXAMPLE: Identify which of the following E2 mechanisms would react to completion. Do not draw final products. a. b. c. d. Page 4
PRACTICE: Provide the full mechanism and draw the final product for the following E2 reactions. a. b. c. Page 5
CONCEPT: THE E1 MECHANISM A weak nucleophile reacts with an inaccessible leaving group to produce beta-elimination in two-steps. E1 Properties (Circle One) Nucleophile = Strong / Weak Leaving Group = Unsubstituted / Highly Substituted Reaction coordinate = Transition State / Intermediate Reaction = Concerted / Two-Step Rate = Unimolecular / Bimolecular Rate = k[rx] / k[nu][rx] Stereochemistry = Page 6
PRACTICE: Provide the full mechanism and draw the final product for the following reactions. a. b. Page 7
CONCEPT: SOLVENTS Solvents are mostly inert compounds that provide a medium for the reaction to take place in. Although extremely important in lab, they rarely affect the outcome of a written reaction in Orgo 1 Classification of Solvents Polar solvents are solvents which contain a Aprotic solvents are solvents that cannot display Protic solvents are solvents that display (stabilize carbocations, hinder nucleophiles) Therefore, we will prefer to run & in protic solvents, and & in aprotic solvents. EXAMPLE: Identify the following solvents as apolar, polar aprotic or polar protic Page 8
CONCEPT: LEAVING GROUPS AND NUCLEOPHILES Leaving Groups: Alkyl halides are the most common leaving groups of organic chemistry, but there are others. Sulfonate Esters are the name given to a group of leaving groups with the general formula -SO3R Water is also a common leaving group, usually formed after alcohol is protonated with a strong acid Page 9
Nucleophile: Molecule that can easily donate electrons Base: Molecule that can easily remove a proton Relative Strength Rules: 1. A negative charge will always be a stronger nucleophile than its neutral counterpart. 2. The bulkier the substrate, the more and less it is. 3. Page 10
CONCEPT: THE BIG DADDY MECHANISM FLOWCHART Mechanisms are rarely given. We use nucleophile and leaving group information to determine the favored mechanism. Page 11
PRACTICE: Predict the mechanism for the following reactions. Provide the full mechanism and draw the final product. a. b. c. Page 12
PRACTICE: Predict the mechanism for the following reactions. Provide the full mechanism and draw the final product. d. e. f. Page 13