Question

Relation between reactant and major product obtained in the following reaction is CC(=O)CCCC(C)=O \(\frac{\text { (i) } 8 \mathrm{H} / \Delta \text { (ii) } \mathrm{N}_{2} \mathrm{H}_{4}}{\text { (iii) } \mathrm{O} \mathrm{H} / \Delta \text { (iv) } \mathrm{O}_{3}, \mathrm{Zn}}\) (A) Position isomers (B) Functional isomers (C) Chain isomers (D) Not isomers

Short answer

The reactant and major product in the given reaction are related as functional isomers. The correct answer is (B) Functional isomers.

Step-by-step solution

Identify the starting compound

The given SMILES representation, "CC(=O)CCCC(C)=O", corresponds to the structure of 6-oxoheptanoic acid, an organic compound with a carboxylic acid and a ketone functional group. The structure looks like this: H3C-C(=O)-CH2-CH2-CH2-CH2-C(=O)-OH

Investigate the first reaction step (i: 8H/Δ)

The first reaction step uses 8H and heat (Δ). This reaction, known as Clemmensen reduction, reduces the ketone group to an alkyl group: H3C-C(=O)-CH2-CH2-CH2-CH2-C(=O)-OH → H3C-CH2-CH2-CH2-CH2-CH2-C(=O)-OH

Investigate the second reaction step (ii: N2H4)

The second reaction step adds hydrazine (N2H4) to the mixture. This reaction, called Wolff-Kishner reduction, reduces the carbonyl group to a methylene group: H3C-CH2-CH2-CH2-CH2-CH2-C(=O)-OH → H3C-CH2-CH2-CH2-CH2-CH2-CH2-OH

Investigate the third reaction step (iii: OH/Δ)

The third reaction step adds a hydroxide ion (OH-) and heat (Δ). In this step, the carboxylic acid group is converted to an alkene through α,β-unsaturated acid dehydration: H3C-CH2-CH2-CH2-CH2-CH2-CH2-OH → H2C=CH-CH2-CH2-CH2-CH3

Investigate the fourth reaction step (iv: O3, Zn)

The last reaction step involves ozone (O3) and zinc (Zn) as reagents. This step is known as an ozonolysis reaction, which cleaves the double bond in the alkene: H2C=CH-CH2-CH2-CH2-CH3 → H2C=O + H3C-CH2-C=O

Compare the reactant and major product

Now, let's compare the original reactant (6-oxoheptanoic acid) and the major product (2 smaller molecules: formaldehyde and butanal). These two products are related but have different functional groups. Formaldehyde has an aldehyde group (-C=O) and butanal also has an aldehyde group. The reactant and major product are related as functional isomers since they have the same molecular formula but different functional groups. So, the correct answer is (B) Functional isomers.

Key concepts

SMILES Notation in Organic Chemistry

SMILES (Simplified Molecular Input Line Entry System) is a way of representing molecular structures using short ASCII strings. It's used widely in computational chemistry and cheminformatics to describe the structure of a molecule efficiently. SMILES notation simplifies the representation of molecular and chemical data into a linear form.
SMILES strings encode the atom and bond information required to recreate the molecular structure:

• Atoms are represented by their chemical symbols.
• Bonds are usually implied by the order of the letters, but double and triple bonds can be indicated with "=" and "#" respectively.
• Branches and cyclic structures are described using specific punctuation symbols like parentheses and numbers.

Understanding SMILES allows chemists to quickly convey complex molecular structures and easily input them into databases or software for further analysis and prediction of chemical properties.

Clemmensen Reduction

Clemmensen reduction is a chemical reaction used to convert carbonyl compounds, such as ketones and aldehydes, into hydrocarbons. This process is very effective for compounds that are stable under acidic conditions.
Typically, Clemmensen reduction involves the reaction of the carbonyl compound with zinc amalgam and concentrated hydrochloric acid. Here's a breakdown of the process:

• The ketone or aldehyde is combined with zinc amalgam, a combination of zinc and mercury.
• Concentrated hydrochloric acid is applied, which facilitates the reduction.
• The carbonyl group (C=O) is transformed into a methylene group (CH₂).

This reaction is generally used when single-step reduction directly to alkanes is desired, especially if the substrate is sensitive to strong oxidizing agents. However, it can't be used on substrates sensitive to acidic conditions.

Wolff-Kishner Reduction

The Wolff-Kishner reduction is another method for converting carbonyl groups into methylene groups, specifically in ketones and aldehydes. Unlike Clemmensen, this reduction is performed under basic conditions and uses hydrazine (N₂H₄) as a reagent.
Here's how the Wolff-Kishner reduction works:

• Hydrazine reacts with the carbonyl group to form a hydrazone.
• Under strong basic conditions and heat, nitrogen gas is eliminated.
• This results in the conversion of the carbonyl bond (C=O) into an alkane bond (C-H).

This method is favored for base-stable compounds, as it avoids acidic environments, making it versatile for substrates that do not withstand acidic conditions. This reaction is often a go-to choice when handling acid-sensitive substrates, or when working under conditions where metal catalysts are undesirable.

Ozonolysis Reaction

Ozonolysis is a reaction where ozone (O₃) cleaves alkenes or alkynes to form carbonyl compounds, typically leading to alkenes being converted into aldehydes and ketones.
In an ozonolysis reaction:

• Ozone attacks the double bond of alkenes or alkynes.
• The intermediate ozonide is unstable and is generally reduced using a reductive workup such as zinc and water, or another reducing agent.
• Results in the cleavage of the double bond, producing two carbonyl fragments.

Ozonolysis is a powerful tool in organic synthesis for breaking down complex molecules into smaller, more manageable pieces. It helps elucidate the structure of unsaturated compounds by indicating the positions of double bonds through the identities of the resulting carbonyl products. It is especially useful in characterizing unknown samples or redesigning synthetic pathways.