Ch. 6 - Thermodynamics and KineticsWorksheetSee all chapters
All Chapters
Ch. 1 - A Review of General Chemistry
Ch. 2 - Molecular Representations
Ch. 3 - Acids and Bases
Ch. 4 - Alkanes and Cycloalkanes
Ch. 5 - Chirality
Ch. 6 - Thermodynamics and Kinetics
Ch. 7 - Substitution Reactions
Ch. 8 - Elimination Reactions
Ch. 9 - Alkenes and Alkynes
Ch. 10 - Addition Reactions
Ch. 11 - Radical Reactions
Ch. 12 - Alcohols, Ethers, Epoxides and Thiols
Ch. 13 - Alcohols and Carbonyl Compounds
Ch. 14 - Synthetic Techniques
Ch. 15 - Analytical Techniques: IR, NMR, Mass Spect
Ch. 16 - Conjugated Systems
Ch. 17 - Aromaticity
Ch. 18 - Reactions of Aromatics: EAS and Beyond
Ch. 19 - Aldehydes and Ketones: Nucleophilic Addition
Ch. 20 - Carboxylic Acid Derivatives: NAS
Ch. 21 - Enolate Chemistry: Reactions at the Alpha-Carbon
Ch. 22 - Condensation Chemistry
Ch. 23 - Amines
Ch. 24 - Carbohydrates
Ch. 25 - Phenols
Ch. 26 - Amino Acids, Peptides, and Proteins

Carbocations will rearrange to an adjacent, more stable position if possible. These have different names based on which atoms are rearranging.

Concept #1: Understanding why carbocations shift.

a. 1,2-Hydride Shift occurs when there is a hydrogen located on an adjacent, more stable carbon.

Concept #2: Carbocation Rearrangments

b. 1,2-Alkyl Shift occurs when only small alkyl groups are located on an adjacent, more stable carbon.

Concept #3: Carbocation Rearrangements

c. Ring Expansion occurs when a carbocation is adjacent to a 3, 4 or 5-membered ring.

Concept #4: Carbocation Rearrangements

I hope we didn't lose you with that last one! Just remember to label your carbons and you will do great. :)



NOW, we will move on to some practice questions. Let's see if we can apply what we just learned to different molecules who may or may not want to undergo a rearrangment. 

Concept #5: Intro

Which of the following carbocations are likely to rearrange?

Practice: Which of the following carbocations would be likely to rearrange? Draw each rearranged structure below.

Molecule I

Practice: Which of the following carbocations would be likely to rearrange? Draw each rearranged structure below.

Molecule II

Practice: Which of the following carbocations would be likely to rearrange? Draw each rearranged structure below.

Molecule III

Practice: Which of the following carbocations would be likely to rearrange? Draw each rearranged structure below.

Molecule IV

So, how'd you do? 

 

I know you guys rocked it. Let's move on. 

Additional Problems
When compound shown below is exposed to an acid, a molecule of water is eliminated, and a structural rearrangement ensues. The final product is a ketone with a molecular formula C18H18O. However, despite the fact that there are two –OH groups in the starting material, only one ketone is produced, with greater than 99% selectivity. Draw (a) the structure of that ketone and (b) the detailed mechanism that explains its formation. Then (c) provide a brief explanation why no other products are formed. Show all charges and intermediates, and use curved arrows to indicate the flow of electrons. Do not draw transition states.
Which carbocation would not be likely to undergo rearrangement?
Predict whether each of the following carbocations will rearrange. If so, draw the expected rearrangement using curved arrows.
Predict whether each of the following carbocations will rearrange. If so, draw the expected rearrangement using curved arrows.
In the acid-catalyzed dehydration of 2-methyl-1-propanol, what carbocation would be formed if a hydride shift accompanied cleavage of the carbon–oxygen bond in the alkyloxonium ion? What ion would be formed as a result of a methyl shift? Which pathway do you think will predominate, a hydride shift or a methyl shift?
Each of the following carbocations has the potential to rearrange to a more stable one. Write the structure of the rearranged carbocation, and use curved arrows to show how it is formed.  
Each of the following carbocations has the potential to rearrange to a more stable one. Write the structure of the rearranged carbocation, and use curved arrows to show how it is formed.   
Each of the following carbocations has the potential to rearrange to a more stable one. Write the structure of the rearranged carbocation, and use curved arrows to show how it is formed. 
Each of the following carbocations has the potential to rearrange to a more stable one. Write the structure of the rearranged carbocation, and use curved arrows to show how it is formed. 
Each of the following carbocations has the potential to rearrange to a more stable one. Write the structure of the rearranged carbocation, and use curved arrows to show how it is formed.  
In Problem 5.20 (Section 5.13) we saw that acid-catalyzed dehydration of 2,2- dimethylcyclohexanol afforded 1,2-dimethylcyclohexene. To explain this product we must write a mechanism for the reaction in which a methyl shift transforms a secondary carbocation to a tertiary one. Another product of the dehydration of 2,2-dimethylcyclohexanol is isopropylidenecyclopentane. Write a mechanism to rationalize its formation, using curved arrows to show the flow of electrons.   
(+)-Aureol is a natural product that shows selective anticancer activity against certain strains of lung cancer and colon cancer. A key step in the biosynthesis of (+)-aureol (how nature makes the molecule) is believed to involve the conversion of carbocation A to carbocation B (Org. Lett. 2012, 14, 4710–4713). Propose a possible mechanism for this transformation and explain the observed stereochemical outcome. 
Predict whether each of the following carbocations will rearrange. If so, draw the expected rearrangement using curved arrows.
The following carbocation is one that could form in the hydrochlorination of 3, 3-dimethyl-1-butene: Classify this carbocation as primary, secondary, or tertiary: ___________Is this cation more stable, less stable, or equally stable to the other carbocation that could form? _________
The following carbocation is one that could form in the acid catalyzed hydration of 1-methyleyclopentene: Classify this carbocation as primary, secondary, or tertiary: ___________Is this cation more stable, less stable, or equally stable to the other carbocation that could form? _________