Questions and Answers
What is the purpose of dehydrating cyclohexanol in this experiment?
To form cyclohexene in an elimination reaction.
What occurs in the first step of the dehydration reaction?
The -OH is protonated to form a protonated alcohol.
What are azeotropes?
Mixtures of two liquids that have a single sharp boiling point.
What indicates a positive bromine test?
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What is observed in the permanganate test for alkenes and alkynes?
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What should you do if concentrated acid is spilled during the experiment?
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Which of the following are true statements about bromine (Br2)? (Select all that apply)
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What should you do if your skin comes in contact with HCl?
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Match the density of the following solvents from most to least dense:
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What indicates the presence of an alkane in the bromine test?
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How can you determine whether a reaction has occurred in the experiment?
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Why is concentrated HCl a poor choice as the acid catalyst for the dehydration of cyclohexanol?
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What type of reaction do bromine and permanganate undergo with cyclohexene?
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Why is the reaction of cyclohexene with HBr not useful for characterization?
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What does a 'dry' distilling flask mean for the experiment?
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Why is acetone not suitable as a solvent for extraction from water?
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Which of the following statements about E2 reactions are true? (Select all that apply)
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What should you do if you spill sulfuric acid on your hand?
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Which of the following is used for the treatment of reagent spills in the laboratory?
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What is the rate-determining step of the dehydration of cyclohexanol?
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What is the similarity between E2 elimination and SN2 substitution?
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What occurs during the formation of 3-chloro-3,7-dimethyloctane from 3,7-dimethyl-3-octanol?
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What solution should be used after rinsing sulfuric acid from the skin?
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Study Notes
Dehydration of Cyclohexanol
- Cyclohexanol is dehydrated using acid catalysis to produce cyclohexene through an elimination reaction, specifically an E1 mechanism.
- Water is lost during the reaction, creating a carbon-carbon π-bond.
Reaction Steps
- Protonation: The hydroxyl group (-OH) of cyclohexanol is protonated, forming a better leaving group (water).
- Carbocation Formation: The protonated alcohol undergoes dehydration, losing water and forming a carbocation. The rate of this step determines the reaction rate.
- Deprotonation: The carbocation rapidly loses a proton to yield cyclohexene.
Azeotropes
- Azeotropes are mixtures with a distinct boiling point that cannot be separated by distillation.
- Multiple-component mixtures (three or four compounds) can also form azeotropes.
Bromine Test
- A positive bromine test for unsaturation occurs when the reddish color of bromine is rapidly discharged, indicating the presence of alkenes.
Permanganate Test (Baeyer's Test)
- For alkenes and alkynes, a deep purple color from permanganate disappears, forming brown manganese dioxide as a precipitate.
Spill Protocols
- Concentrated acid spills should be neutralized with sodium bicarbonate.
- Immediate reporting and washing with copious amounts of water is crucial if there’s contact with HCl.
Density and Solvent Properties
- Density ranking: chloroform > dichloromethane > water > diethyl ether > hexanes.
- Acetone is unsuitable for extracting organic materials from water due to its miscibility.
Safety Measures
- Bromine is hazardous: causes skin burns and may be fatal if inhaled; gloves are required for handling.
- Rinse sulfuric acid spills with cold water followed by sodium bicarbonate solution.
Reaction Characteristics
- E2 reactions are stereospecific; strong bases enhance elimination reactions.
- Formation of 3-chloro-3,7-dimethyloctane from 3,7-dimethyl-3-octanol involves initial protonation leading to water release.
Comparisons
- Both E2 eliminations and SN2 substitutions are influenced by nucleophile concentration.
- Concentrated HCl is suboptimal for cyclohexene formation due to potential carbocation bond formation instead of double bond formation.
Distillation Practices
- Distillation should not be continued until the flask is completely dry, meaning lacking all materials, not just water.
Indicators for Reaction Occurrence
- Successful dehydration is indicated by the separation of product layers — cyclohexene forms the top layer while the aqueous layer remains below.
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Description
In this quiz, you will explore the dehydration of cyclohexanol to cyclohexene through an acid-catalyzed elimination reaction. This process involves the formation of a carbon-carbon π-bond via an E1 mechanism. Test your understanding of the concepts and steps involved in this chemical reaction.