Problem 38 - A Complete Resource Book in Chemistry for JEE Main

Question

Which is not a product when O=C1C(O)CCC(O)C1O is treated with \(\mathrm{HIO}_{4} ?\) (a) \(\mathrm{HCOOH}\) (b) \(\mathrm{H}_{2} \mathrm{O}\) (c) \(\mathrm{HCHO}\) (d) \(\mathrm{CO}_{2}\)

Step-by-Step Solution

Answer

The answer is (b) \(\mathrm{H}_{2}\mathrm{O}\); it is not a direct product of \(\mathrm{HIO}_{4}\) cleavage.

Step 1: Understand the Reactant Structure

The given molecule is a cyclic 1,2,3-trihydroxy cyclohexanone. It's important to recognize that periodic acid cleavage is effective on vicinal diols (neighboring OH groups). Therefore, we need to identify the diol configuration within the molecule.

Step 2: Identify Cleavage Sites

In the cyclic 1,2,3-trihydroxy cyclohexanone, the 1,2 and 2,3 positions have vicinal diol pairs which can be cleaved by \(\mathrm{HIO}_{4}\). Hence, the 1,2 and 2,3 diols will be opened during the reaction.

Step 3: Predict the Cleavage Products

Cleavage of 1,2-diol leads to the formation of formaldehyde (HCHO). The 2,3-diol cleavage will generate formic acid (HCOOH) and carbon dioxide (CO2). The reaction generally results in the release of water (H2O) as well. Identify these as potential products.

Step 4: Identify Non-Product

From the products identified in Step 3: HCHO (formaldehyde), HCOOH (formic acid), CO2, and H2O, all are observed products. Given the options: (a) HCOOH, (b) H2O, (c) HCHO, (d) CO2, all match the predicted products from Step 3. Analyze and identify the option that does not fit.

Step 5: Conclusion

Since all listed options (a, b, c, d) appear as products, we check for options that are not cleavage products. H2O does not directly appear as a distinct product from the diol cleavage. Rather, it might be produced as a byproduct or not present, indicating it could be the non-distinct diol cleavage product.

Key Concepts

Vicinal Diols

Vicinal diols are an essential concept in organic chemistry, especially when dealing with oxidation reactions such as those involving periodic acid cleavage. These are molecules that have two hydroxyl groups (OH groups) attached to adjacent carbon atoms, also known as 1,2-diols. They play a crucial role in the cleavage reactions.
When exposed to oxidizing agents like periodic acid (\( \mathrm{HIO}_{4} \)), these vicinal diols can be broken down into smaller molecules. This property makes them useful for pinpointing specific sites within a molecule that can be cleaved to yield different products.

• Periodic acid selectively targets vicinal diols.
• The cleavage results in breaking the C-C bond between the two carbon atoms holding the OH groups.
• This often creates distinct, smaller carbonyl-containing products such as aldehydes or ketones.

Understanding the placement and presence of vicinal diols is essential in predicting the outcome of reaction pathways leveraging periodic acid cleavage.

Cyclic Compounds

Cyclic compounds are chemical structures where the atoms are connected in a closed loop or ring. They are prevalent in both natural and synthetic compounds and often exhibit unique chemical properties. This exercise involves understanding these cyclic structures in the context of periodic acid reactions.
In the given example, we are dealing with a cyclic structure known as 1,2,3-trihydroxy cyclohexanone. This molecule consists of a six-membered ring with hydroxyl groups present on three consecutive carbon atoms, an example of a polyhydroxy cyclic compound.

• The configuration of the hydroxyl groups in the ring allows specific cleavage points.
• Cyclic compounds can occasionally complicate cleavage reactions as the cyclic nature impacts how bonds are broken and reformed.
• The cleavage often results in opening the ring at the points of bond breaking, leading to linear or smaller cyclic fragments.

It is crucial to properly understand the spatial orientation of hydroxyl groups in cyclic compounds to predict the cleavage reactions accurately.

Cleavage Reactions

Cleavage reactions are chemical reactions where a molecule is split into smaller parts. This process is highly relevant in biochemistry and organic synthesis, as it leads to the breakdown of complex molecules into simpler ones.
When dealing with periodic acid (\( \mathrm{HIO}_{4} \)), the cleavage specifically targets vicinal diols, breaking the carbon-carbon bond between them and converting the diol into two carbonyl-containing groups such as aldehydes or carboxylic acids. This reaction is quite selective and can provide insights into the structure of complex molecules when used analytically.

• When a vicinal diol is cleaved, each OH group is initially oxidized to a carbonyl group.
• In the case of cyclic compounds, cleavage might result in the ring opening.
• Final products may include a mix of aldehydes, carboxylic acids, and sometimes release of gases like \( \mathrm{CO}_{2} \).

Understanding cleavage reactions allows chemists to simplify complex structures and analyze or utilize fragments for further reactions or in synthetic applications.