Question

Cyclohexene on ozonolysis followed by reaction with zinc dust and water gives compound E. Compound \(\mathbf{E}\) on further treatment with aqueous KOH yields compound F. Compound \(\mathbf{F}\) is (A) O=CC1=CCCC1 (B) O=CC1C=CCC1 (C) O=C(O)C1C=CCC1 (D) O=C(O)CCCCC(=O)O

Short answer

Compound F is C, O=C(O)C1C=CCC1.

Step-by-step solution

Perform Ozonolysis on Cyclohexene

Ozonolysis cleaves the double bond in cyclohexene and introduces two oxygen atoms, one at each carbon that originally formed the double bond. This forms an ozonide intermediate, which is then reduced by zinc dust in the presence of water to give two carbonyl compounds.

Reduction of Ozonide Intermediate

Reduction of the ozonide with zinc dust and water will typically break down the ozonide into aldehydes or ketones. In the case of cyclohexene, this will result in the formation of two molecules of the simplest possible aldehyde, formaldehyde (compound E), as the original molecule had no additional substituents on the double bond.

React Compound E with Aqueous KOH

Aqueous KOH is basic and will cause the Cannizzaro reaction to occur with concentrated solutions of formaldehyde. Since aldehydes without alpha-hydrogen atoms (like formaldehyde) undergo the Cannizzaro reaction with strong bases, compound E will be transformed into methanol and formate ion.

Identify Compound F

After the reaction with KOH, the formate ion can be neutralized to form formic acid. Formic acid has a structure of O=C(O)H, which means when two formic acid molecules are produced from each formaldehyde molecule, we end up with option (C) O=C(O)C1C=CCC1 as the correct structure for compound F, as it corresponds to the molecular formula and structure of formic acid.

Key concepts

Ozonolysis

Ozonolysis is a powerful organic chemistry reaction used to cleave double bonds by reacting them with ozone, forming ozonides as reaction intermediates. This reaction is particularly useful for discerning the structure of unknown alkenes since it breaks them down into simpler carbonyl compounds.

When an alkene like cyclohexene undergoes ozonolysis, it's essentially 'cut' at the double bond. Each carbon atom from the double bond will get an oxygen attached, resulting in the formation of two carbonyl functional groups. Depending on the conditions, these can be further reduced to aldehydes or ketones. In the case of our exercise, zinc dust and water are used to reduce the ozonide, leading mostly to the formation of aldehydes, which are simpler compounds with a carbonyl group bonded to a hydrogen atom.

Cannizzaro Reaction

The Cannizzaro reaction is a classic example of a redox reaction in organic chemistry where aldehydes that lack alpha-hydrogen atoms, such as formaldehyde, are induced to react with a strong base to form a primary alcohol and a carboxylic acid salt. In presence of aqueous KOH, formaldehyde is disproportionated, meaning it acts as both an oxidizing agent and as a reducing agent within the same molecule.

This reaction is particularly notable because it introduces the concept of molecule self-transformation under basic conditions. For students, understanding the Cannizzaro reaction helps in grasping how unprotected aldehydes can behave under strongly basic conditions, which is a key concept in the functional group transformations of organic chemistry.

Organic Chemistry Reaction Mechanisms

Understanding organic chemistry reaction mechanisms is essential to predict the outcome of chemical reactions and to design synthesis pathways for desired molecules. A reaction mechanism describes the step-by-step sequence by which reactants transform into products. It involves the movement of electrons, the formation and breaking of bonds, and the intermediates formed during the course of the reaction.

In our exercise with cyclohexene, the reaction mechanism for ozonolysis involves the formation of an ozonide intermediate, which subsequently breaks down into carbonyl compounds. In the Cannizzaro reaction, the mechanism involves the transfer of a hydride ion from one formaldehyde molecule to another. By learning these mechanisms, students can visualize and understand the subtleties of each step in a reaction, which is vital for mastering organic chemistry.

Identification of Organic Compounds

The identification of organic compounds is a fundamental aspect of organic chemistry. It involves analyzing structures, functional groups and, often, the reaction behavior of compounds. Techniques like spectroscopy, chromatography, and various qualitative tests provide data that, when combined with knowledge of reaction mechanisms, can help deduce the structure of an unknown compound.

In our exercise, by knowing the reaction mechanisms of ozonolysis and the Cannizzaro reaction, we were able to logically identify the product as formic acid. This deductive process is the essence of organic compound identification, a skill that is honed over time with practice and deep understanding of organic reactions.