30: Rearrangements
- Page ID
- 151241
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Template:HideTOCFunky Rearrangements
PASSPORT: Review Hydride Shifts
1,2 Hydride Shifts
The reaction of 3-methyl-1-butene with HCl gives 40% of 2-chloro-3-methylbutane product and 60% of the 2-chloro-2-methylbutane product.
- Draw a mechanism to explain these results.
Rearrangements are extraordinarily common in carbocation chemistry. 1,2 –migration of hydride (hydride shifts) are among the fast reactions known.
- When and why do these reactions occur readily?
Meerwein-Wagner Rearrangements
Alkyl Shifts (Meerwein-Wagner Rearrangements) are also common.
- Write a mechanism for the following reaction:
- Write a mechanism for the following reaction:
Rearrangements to Electron Deficient Centers
(Almost Cationic)
Pinacol Rearrangement
- Provide a mechanism for the following transformation
-
Why is th Pinacol Rearrangement favored over an elimination or a substitution reaction?
Beckman rearrangement
This rearrangement begins with the use of an oxime
- Review: How would you make the oxime?
-
Provide a mechanism for the following transformation. Remember alkyl shifts will move to carbocation centers or other electron deficient atoms.
Baeyer-Villager Rearrangement
- Provide a mechanism for the following transformation. Remember alkyl shifts will move to carbocation centers or other electron deficient atoms.
-
Review: When have you seen this reagent before? What other reactions does it do?
Wolff Rearrangment
- Draw Lewis electron dot structure for diazomethane, CH2N2.
- Provide the mechanism for the following transformation
- Provide a mechanism for the following transformation. Remember alkyl shifts will move to carbocation centers or other electron deficient atoms.
This reaction is quenched with nucleopholes such as water.
- Draw the product for the reaction of the ketene above with water.
- This carbene intermediate can be used in other ways. Using what you know about carbenes, predict what the product of this reaction will be.
Curtius Rearrangement
This is almost the same reaction except that sodium azide is added rather than diazomethane.
- Draw Lewis electron dot structure for sodium azide, NaN3.
- Provide a mechanism for the following transformation.
-
The isocyanate product above is very sensitive to nucleophilic attack. Draw the reaction of this isocyanate with methanol
Hoffman Rearrangement
The Hoffman rearrangement also involves the formation of an isocyanate in a related rearrangement.
- Provide a mechanism for the following transformation
The isocyanate product above quickly reacts with the OH- in solution to form the carbamic acid.
- Draw the product formed
Carbamic acid is quickly deprotonated and spontaneously decarboxylates to form a primary amine.
- Draw this mechanism
Summary Page
Additional Problems
- The synthesis of Perhydrohistrionicotoxin by E.J. Corey in 1975 displays the utility of some of these rearrangements.
-
Draw mechanisms for the following changes.
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Provide a mechanism for the following transformation of morphine into apomorphine. Remember Meerwein-Wagner Rearrangemnts, This is hard!
