Question

A compound has the empirical formula \(\mathrm{C}_{5} \mathrm{H}_{12} \mathrm{O} .\) Upon controlled oxidation, it is converted into a compound of empirical formula \(\mathrm{C}_{5} \mathrm{H}_{10} \mathrm{O},\) which behaves as a ketone. Draw possible structures for the original compound and the final compound.

Short answer

The original compound could be 2-pentanol and the final compound 2-pentanone.

Step-by-step solution

Understanding Empirical Formulas

The empirical formula of a compound gives the simplest whole number ratio of atoms in the compound. The given empirical formula for the original compound is \( \mathrm{C}_5 \mathrm{H}_{12} \mathrm{O} \). This means for every 5 carbon atoms, there are 12 hydrogen atoms and 1 oxygen atom. Similarly, the final compound's empirical formula is \( \mathrm{C}_5 \mathrm{H}_{10} \mathrm{O} \).

Analyzing the Change from Original to Final Compound

The original compound has more hydrogen atoms than the final compound. The conversion of \( \mathrm{C}_5 \mathrm{H}_{12} \mathrm{O} \) to \( \mathrm{C}_5 \mathrm{H}_{10} \mathrm{O} \) indicates a reduction of 2 hydrogen atoms, suggesting oxidation where either a double bond or a new group is introduced.

Understanding Ketones

Ketones are compounds where a carbonyl group (\( \mathrm{C}=\mathrm{O} \)) is bonded to two carbon atoms. For the final compound to be a ketone, it must contain this carbonyl group as part of its new structure, explaining the reduction in hydrogen count.

Drawing Possible Structures for Original Compound

The original compound, with the formula \( \mathrm{C}_5 \mathrm{H}_{12} \mathrm{O} \), can be an alcohol since it can be oxidized to form a ketone. Possible structures involve the alcohol group (\(-\mathrm{OH}\)) seen in positions such as 2-pentanol (with the hydroxyl group on the second carbon): \( \text{C-C-C(COH)-C} \) with varying positions of attachment, maintaining the empirical formula.

Drawing Possible Structures for the Final Compound

The final compound that behaves as a ketone, with the empirical formula \( \mathrm{C}_5 \mathrm{H}_{10} \mathrm{O} \), will have a carbonyl group positioned to produce a pentanone. An example structure could be 2-pentanone, where the carbonyl is positioned at the second carbon: \( \text{C-C(=O)-C-C-C} \).

Verification of Structures

Each drawn structure should be verified to ensure that it respects the empirical formula, the conversion process through oxidation, and the requirement that the final structure includes a carbonyl group typical of ketones. Both proposed structures meet these conditions.

Key concepts

Oxidation Reactions

Oxidation reactions play a crucial role in organic chemistry. In the context of the given exercise, oxidation involves the change from an alcohol to a ketone. The original compound with empirical formula \( \mathrm{C}_5 \mathrm{H}_{12} \mathrm{O} \) has fewer oxygens and more hydrogens compared to the ketone, hinting that oxidation has taken place.

During oxidation:

• A molecule might lose hydrogen atoms, which happens in this conversion from \( \mathrm{C}_5 \mathrm{H}_{12} \mathrm{O} \) to \( \mathrm{C}_5 \mathrm{H}_{10} \mathrm{O} \).
• The oxidation process introduces a carbonyl group \((\mathrm{C}=\mathrm{O})\), which is the defining feature of ketones.

Understanding oxidation helps in predicting the structural changes a compound undergoes, as is demonstrated in converting an alcohol to a ketone.

Ketone Structure

Ketones are a class of organic compounds characterized by the carbonyl group \((\mathrm{C}=\mathrm{O})\) bonded to two carbon atoms. They are distinct due to their straightforward carbon-oxygen double bond, which falls between two alkyl groups.

To recognize a ketone:

• Look for the carbonyl group \((\mathrm{C}=\mathrm{O})\) located in the middle of the carbon chain.
• Ketones cannot have the carbonyl carbon bonded to hydrogen, differentiating them from aldehydes, which have at least one hydrogen atom bonded to the carbonyl carbon.
• In this exercise, the final compound formed, \( \mathrm{C}_5 \mathrm{H}_{10} \mathrm{O} \), exemplifies a ketone such as 2-pentanone.

The carbon structure around the ketone influences its properties and reactions. For instance, the position of the carbonyl group affects physical properties like boiling point and chemical reactivity.

Alcohol Oxidation

Alcohol oxidation is a chemical reaction where alcohols are converted into other types of compounds, often ketones or aldehydes. This type of reaction is fundamental in organic chemistry because alcohols serve as starting points for synthesizing a variety of other compounds.

In the exercise, the original compound with the empirical formula \( \mathrm{C}_5 \mathrm{H}_{12} \mathrm{O} \) is likely an alcohol. Detailed observations include:

• Alcohols have an \(-\mathrm{OH}\) hydroxyl group attached to one of the carbons in the chain. Possible locations include secondary alcohols like 2-pentanol, where the \(-\mathrm{OH}\) group is on the second carbon.
• Upon oxidation, alcohols lose a pair of hydrogen atoms and the \(-\mathrm{OH}\) group changes to a carbonyl group \( (\mathrm{C}=\mathrm{O}) \), resulting in a ketone or aldehyde. In this exercise, it results in a ketone.

Understanding alcohol oxidation helps predict the products of synthetic reactions and the transformations organic compounds can undergo.