Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy

Wade9th EditionOrganic ChemistryISBN: 9780135213728Not the one you use?Change textbook

Wade 9th Edition

Ch. 15 - Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy

Problem 38a

Chapter 15, Problem 38a

A student was studying terpene synthesis, and she wanted to make the compound shown here. First she converted 3-bromo-6-methylcyclohexene to alcohol A. She heated alcohol A with sulfuric acid and purified one of the components (compound B) from the resulting mixture. Compound B has the correct molecular formula for the desired product.
a. Suggest how 3-bromo-6-methylcyclohexene might be converted to alcohol A.

Verified step by step guidance

Step 1: Analyze the structure of 3-bromo-6-methylcyclohexene. The bromine atom is attached to the cyclohexene ring, and the methyl group is at position 6. To convert this compound to alcohol A, the bromine atom must be replaced with a hydroxyl group (-OH). This suggests a nucleophilic substitution reaction.

Step 2: Choose an appropriate reagent for nucleophilic substitution. A common method to replace a bromine atom with a hydroxyl group is to use aqueous sodium hydroxide (NaOH) or potassium hydroxide (KOH) under heating conditions. This reaction proceeds via an SN2 or SN1 mechanism depending on the reaction conditions and the structure of the substrate.

Step 3: Consider the reaction mechanism. In this case, the cyclohexene ring is allylic, which stabilizes a carbocation intermediate. Therefore, the reaction is likely to proceed via an SN1 mechanism. The bromine atom leaves, forming a carbocation intermediate, which is then attacked by the hydroxide ion to form alcohol A.

Step 4: Verify the structure of alcohol A. The product should have the hydroxyl group (-OH) attached to the same carbon where the bromine atom was originally located. The structure of alcohol A matches this description, with the hydroxyl group replacing the bromine atom.

Step 5: Ensure reaction conditions are suitable. The reaction should be carried out in a polar protic solvent (e.g., water or ethanol) to stabilize the carbocation intermediate and facilitate the nucleophilic attack by hydroxide ions.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Nucleophilic Substitution

Nucleophilic substitution is a fundamental reaction in organic chemistry where a nucleophile attacks an electrophilic carbon atom, replacing a leaving group. In the case of converting 3-bromo-6-methylcyclohexene to alcohol A, a nucleophile, such as hydroxide ion (OH-), can displace the bromine atom, resulting in the formation of an alcohol. This reaction is crucial for understanding how to manipulate functional groups in organic synthesis.

Alcohol Formation

Alcohols are organic compounds characterized by the presence of one or more hydroxyl (-OH) groups. The conversion of alkenes or alkyl halides to alcohols is a common transformation in organic synthesis. In this scenario, the formation of alcohol A from 3-bromo-6-methylcyclohexene involves the addition of water or a hydroxide ion, which is essential for creating the desired functional group for further reactions.

Acid-Catalyzed Dehydration

Acid-catalyzed dehydration is a reaction where an alcohol is converted into an alkene through the removal of a water molecule, typically facilitated by an acid like sulfuric acid. In the context of the question, heating alcohol A with sulfuric acid leads to the formation of compound B, which is an important step in synthesizing the desired terpene. Understanding this mechanism is vital for predicting the products of reactions involving alcohols.

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Related Practice

Textbook Question

The pentadienyl radical, H₂C=CH–CH=CH–CH₂•, has its unpaired electron delocalized over three carbon atoms.

h. Add an electron to the pentadienyl radical to give the pentadienyl anion. Which carbon atoms share the negative charge? Does this picture agree with the resonance picture?

1145

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Textbook Question

The pentadienyl radical, H₂C=CH–CH=CH–CH₂•, has its unpaired electron delocalized over three carbon atoms.

g. Remove the highest-energy electron from the pentadienyl radical to give the pentadienyl cation. Which carbon atoms share the positive charge? Does this picture agree with the resonance picture?

845

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Textbook Question

Determine whether each structure is likely to be colored or not. For those that you predict to be colored, indicate the extended conjugation by marking the series of continuous sp² hybridized atoms.

(a)

(b)

(c)

1180

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Textbook Question

A student was studying terpene synthesis, and she wanted to make the compound shown here. First she converted 3-bromo-6-methylcyclohexene to alcohol A. She heated alcohol A with sulfuric acid and purified one of the components (compound B) from the resulting mixture. Compound B has the correct molecular formula for the desired product.

1469

views

Textbook Question

The pentadienyl radical, H₂C=CH–CH=CH–CH₂•, has its unpaired electron delocalized over three carbon atoms.

f. Show how your molecular orbital picture agrees with the resonance picture showing delocalization of the unpaired electron onto three carbon atoms.

955

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Textbook Question

Determine whether each structure is likely to be colored or not. For those that you predict to be colored, indicate the extended conjugation by marking the series of continuous sp² hybridized atoms.

(d)

(e)

(f)

1283

views