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ORGANIC - MCMURRY 9E
CH.11 - REACTIONS OF ALKYL HALIDES: ELIMINATIONS (PART 2)
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.
ORGANIC - MCMURRY 9E
CH.11 - REACTIONS OF ALKYL HALIDES: ELIMINATIONS (PART 2)
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.
ORGANIC - MCMURRY 9E
CH.11 - REACTIONS OF ALKYL HALIDES: ELIMINATIONS (PART 2)
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.
ORGANIC - MCMURRY 9E
CH.11 - REACTIONS OF ALKYL HALIDES: ELIMINATIONS (PART 2)
Page 4
PRACTICE: Provide the full mechanism and draw the final product for the following E2 reactions.
a.
b.
c.
ORGANIC - MCMURRY 9E
CH.11 - REACTIONS OF ALKYL HALIDES: ELIMINATIONS (PART 2)
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 = ___________________________
ORGANIC - MCMURRY 9E
CH.11 - REACTIONS OF ALKYL HALIDES: ELIMINATIONS (PART 2)
Page 6
PRACTICE: Provide the full mechanism and draw the final product for the following reactions.
a.
b.
ORGANIC - MCMURRY 9E
CH.11 - REACTIONS OF ALKYL HALIDES: ELIMINATIONS (PART 2)
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
ORGANIC - MCMURRY 9E
CH.11 - REACTIONS OF ALKYL HALIDES: ELIMINATIONS (PART 2)
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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
ORGANIC - MCMURRY 9E
CH.11 - REACTIONS OF ALKYL HALIDES: ELIMINATIONS (PART 2)
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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.
ORGANIC - MCMURRY 9E
CH.11 - REACTIONS OF ALKYL HALIDES: ELIMINATIONS (PART 2)
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CONCEPT: THE BIG DADDY MECHANISM FLOWCHART
Mechanisms are rarely given. We use nucleophile and leaving group information to determine the favored mechanism.
ORGANIC - MCMURRY 9E
CH.11 - REACTIONS OF ALKYL HALIDES: ELIMINATIONS (PART 2)
Page 11
PRACTICE: Predict the mechanism for the following reactions. Provide the full mechanism and draw the final product.
a.
b.
c.
ORGANIC - MCMURRY 9E
CH.11 - REACTIONS OF ALKYL HALIDES: ELIMINATIONS (PART 2)
Page 12
PRACTICE: Predict the mechanism for the following reactions. Provide the full mechanism and draw the final product.
d.
e.
f.
ORGANIC - MCMURRY 9E
CH.11 - REACTIONS OF ALKYL HALIDES: ELIMINATIONS (PART 2)
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CONCEPT: ALKENES and ALKYNES
□ Alkenes/Alkynes are named by adding the suffix modifier (-________/-________) to the end of the root.
● Alkenes/alkynes receive ___________________ in numbering alkanes
● Location is assigned to the first double bonded carbon
EXAMPLE: Name the following compound:
a.
ORGANIC - MCMURRY 9E
CH.11 - REACTIONS OF ALKYL HALIDES: ELIMINATIONS (PART 2)
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CONCEPT: STABILITY OF ALKENES
□ Alkenes are also stabilized through _________________________________
● Since this is only possible with -R groups, the more substituted the alkene, the more ________________
EXAMPLE: Rank the following alkenes in order of lowest to highest heat of combustion.
ORGANIC - MCMURRY 9E
CH.11 - REACTIONS OF ALKYL HALIDES: ELIMINATIONS (PART 2)
Page 15
CONCEPT: ELIMINATION AND ZAITSEV’S RULE
□ We often find that an elimination reaction can yield more than one unique alkene as a product.
● The most stable product = ________________ ● The least stable product = ________________
Zaitsev’s Rule explains that we will always favor the more substituted, thermodynamically stable product
□ UNLESS we are using a bulky base. A bulky base promotes the formation of a less substituted, kinetic product
ORGANIC - MCMURRY 9E
CH.11 - REACTIONS OF ALKYL HALIDES: ELIMINATIONS (PART 2)
Page 16
PRACTICE: Predict ALL of the products of the following reactions. Label them as either major or minor if necessary.
a.
b.
ORGANIC - MCMURRY 9E
CH.11 - REACTIONS OF ALKYL HALIDES: ELIMINATIONS (PART 2)
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