Question

Write structural formulas for the major organic product(s) formed by reaction of 1 -methylcyclohexene with each oxidizing agent. (a) \(\mathrm{OsO}_{4} \mathrm{H}_{2} \mathrm{O}_{2}\) (b) \(\mathrm{O}_{3}\) followed by \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{~S}\)

Short answer

Answer: The major organic products formed are: (a) Syn-dihydroxylation with OsO4/H2O2: 1. HO-C(H)-CH3, with an OH group replacing one hydrogen on the top carbon of the double bond. 2. HO-C-CH3, with an OH group replacing one hydrogen on the bottom carbon of the double bond. (b) Ozonolysis with O3 followed by (CH3)2S: CH3(CH2)4C=O, a straight-chain aldehyde with six carbon atoms.

Step-by-step solution

Reaction (a) Syn-dihydroxylation with OsO4/H2O2

In this reaction, syn-dihydroxylation occurs, meaning that both hydroxyl groups are added to the same side of the double bond in the cyclic alkene. To determine the products of this reaction, follow these steps: 1. Identify the double bond in 1-methylcyclohexene. 2. Break the double bond and add two hydroxyl groups (OH) on the same side of the molecule. 3. Write the resulting structural formula.

Reaction (b) Ozonolysis with O3 followed by (CH3)2S

Ozonolysis is a process in which the double bond is cleaved, and a new functional group is formed, where the double bond was present. In this case, the reduction agent used is (CH3)2S, resulting in aldehydes or ketones. To determine the products of this reaction, follow these steps: 1. Identify the double bond in 1-methylcyclohexene. 2. Break the double bond and add an oxygen atom to each carbon atom that was part of the double bond. 3. Write the resulting structural formula, considering that the carbonyl group (C=O) is formed without migration of any existing group in the molecule. Now that we've gone through the step-by-step process for each reaction, let's write the resulting structural formulas for the products of each reaction.

Products of Reaction (a) Syn-dihydroxylation with OsO4/H2O2

The resulting structural formulas for the major products of the syn-dihydroxylation reaction are: 1. \(\begin{array}{c} \mathrm{H}\mathrm{O-}\underset{\strut|\mathrm{H}}{\mathrm{\overset{\mathrm{H}}{\mathrm{|}}}} \mathrm{C}-\mathrm{CH}_{3} \\ | \\ \mathrm{OH} \end{array}\) 2. \(\begin{array}{c}\mathrm{H}\mathrm{O-}\underset{\qquad|\mathrm{H}}{\mathrm{C}-\mathrm{CH}_{3}}\mathrm{\overset{\mathrm{H}}{\mathrm{|}}}\\ | \\ \mathrm{OH} \end{array}\)

Products of Reaction (b) Ozonolysis with O3 followed by (CH3)2S

The resulting structural formula for the major product of the ozonolysis reaction is: \(\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{4}\mathrm{C}=\mathrm{O}\)

Key concepts

Syn-Dihydroxylation

Syn-dihydroxylation is an essential addition reaction in organic chemistry wherein two hydroxyl (-OH) groups are added to the same side of a carbon-carbon double bond. This reaction transforms an alkene into a vicinal diol, which means the hydroxyl groups are on adjacent carbons. In the context of our exercise, OsO4 (osmium tetroxide) is used as a catalyst, and H2O2 (hydrogen peroxide) serves as the oxidizing agent, enabling the transformation of 1-methylcyclohexene into a diol.

Let's detail the mechanism:

• The alkene's double bond coordinates with the OsO4, creating a cyclic osmate ester intermediate.
• Next, hydrogen peroxide reacts with this intermediate, thereby cleaving the osmium complex and installing two hydroxyl groups syn to each other.
• Finally, we obtain the diol, with the structural formula depicting hydroxyl groups added to the same face of the cyclohexene ring.

Understanding syn-dihydroxylation can help in predicting the structures of products in organic synthesis and explaining the stereochemical outcomes of reactions.

Ozonolysis

Ozonolysis is a reaction where ozone (O3) cleaves the carbon-carbon double bonds in alkenes, forming carbonyl compounds such as aldehydes or ketones. In our case, 1-methylcyclohexene undergoes ozonolysis, showcasing how this oxidative cleavage operates:

The procedure is straightforward but involves an intricate interplay of molecules:

• Ozone interacts with the alkene to form a molozonide, which is an unstable intermediate.
• This molozonide decomposes into a carbonyl compound and a carbonyl oxide, a.k.a. a zwitterionic species.
• (CH3)2S (dimethyl sulfide) is the reducing agent applied after ozone, known for converting any remaining ozonides into their respective carbonyl compounds.
• The final structural formula displays the cleaved double bond replaced by a carbonyl group (C=O) attached to the former alkene carbons.

By becoming familiar with ozonolysis, students can predict the outcome when alkenes are treated with ozone, which is invaluable in synthetic organic chemistry.

Structural Formulas

Structural formulas are graphical representations of molecules showing the arrangement of atoms and the bonds between them. They can range from simplistic skeletal structures to fully fleshed detail including stereochemistry. In an educational setting, understanding these diagrams allows students to visualize complex organic molecules and interpret reaction mechanisms.

For example:

• In syn-dihydroxylation, the structural formula would show the cyclohexene ring with two hydroxyl groups added to adjacent carbon atoms on the same side.
• After ozonolysis, the structural difference is clear, indicating the double bond has been cleaved and converted into a carbonyl group.

Imparting the ability to read and write structural formulas accurately is crucial for students, as this skill forms the foundation for mastering organic chemistry.

Oxidizing Agents

Oxidizing agents are substances that can accept electrons during a chemical reaction, facilitating the oxidation of another species. In organic chemistry, oxidizing agents are key to transforming functional groups through various reactions:

• OsO4 and H2O2 work in tandem in syn-dihydroxylation. OsO4 catalyzes the reaction, while H2O2 provides the necessary oxygen for hydroxyl group attachment.
• Ozone, O3, acts as a powerful oxidizing agent in ozonolysis, breaking double bonds to form new oxidized products.

Understanding the role of oxidizing agents helps students predict and explain how and why certain chemical transformations take place, which is pivotal when considering reaction mechanisms and pathways for synthesis in organic chemistry.