Question

Three different organic compounds have the formula \(\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O}\). Only two of these isomers react with \(\mathrm{KMnO}_{4}\) (a strong oxidizing agent). What are the names of the products when these isomers react with excess \(\mathrm{KMnO}_{4} ?\)

Short answer

The products formed when the two reactive isomers of \(C_3H_8O\) (propan-1-ol and propan-2-ol) react with excess \(\mathrm{KMnO}_4\) are propanoic acid and propanone, respectively.

Step-by-step solution

Oxidation of Propan-1-ol

Propan-1-ol \((CH_3-CH_2-CH_2OH)\) is a primary alcohol, and primary alcohols are oxidized by \(\mathrm{KMnO}_4\) to first aldehydes and then further to carboxylic acids. In this case, propan-1-ol will first be oxidized to propanal, and in the excess of \(\mathrm{KMnO}_4\), propanal will be further oxidized to propanoic acid. Hence, the product formed when propan-1-ol reacts with excess \(\mathrm{KMnO}_4\) is propanoic acid.

Oxidation of Propan-2-ol

Propan-2-ol \((CH_3-CHOH-CH_3)\) is a secondary alcohol, and secondary alcohols are oxidized by \(\mathrm{KMnO}_4\) to ketones. In this case, propan-2-ol will be oxidized to propanone. Hence, the product formed when propan-2-ol reacts with excess \(\mathrm{KMnO}_4\) is propanone. Thus, the products formed when the two reactive isomers of \(C_3H_8O\) (propan-1-ol and propan-2-ol) react with excess \(\mathrm{KMnO}_4\) are propanoic acid and propanone, respectively.

Key concepts

Isomers

Isomers are molecules that have the same molecular formula but different structures or arrangements of atoms. In simpler terms, they contain the same number of atoms of each element but these atoms are connected or organized differently. This difference in arrangement can significantly change the properties and reactivity of the compounds.

In the context of the exercise, three organic compounds with the formula \( \mathrm{C}_{3}\mathrm{H}_{8}\mathrm{O} \) are structural isomers. These include propan-1-ol, propan-2-ol, and methoxyethane. Each isomer has unique properties and reacts differently with chemical agents. For instance, while propan-1-ol and propan-2-ol are alcohols (important for oxidation reactions), methoxyethane is an ether and does not participate in the same oxidation reactions.

Oxidation Reactions

Oxidation reactions involve the loss of electrons or an increase in oxidation state by a molecule, atom, or ion. In organic chemistry, oxidation often refers to the conversion of alcohols into aldehydes, ketones, or carboxylic acids.

With a strong oxidizing agent like potassium permanganate (\( \mathrm{KMnO}_4 \)), primary alcohols (like propan-1-ol) can be oxidized to aldehydes and further to carboxylic acids, while secondary alcohols (such as propan-2-ol) can be oxidized to ketones. The difference in oxidation results is due to the nature of each alcohol and their position within the isomer structure. Primary alcohols have the hydroxyl group at the end of the chain, allowing for further oxidation to carboxylic acids. Secondary alcohols, having the hydroxyl group within the chain, are usually oxidized only to ketones.

Functional Groups

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. Understanding functional groups is crucial as they dictate how a compound will behave in chemical reactions.

In our case, the alcohol group (-OH) in propan-1-ol and propan-2-ol is a functional group that makes these compounds capable of oxidation reactions. Primary alcohols have their -OH group attached to a carbon atom that is itself attached to only one other carbon atom, while secondary alcohols have their -OH group attached to a carbon that is connected to two other carbon atoms. This distinction leads to different oxidation products - for example, carboxylic acids from primary alcohols due to the full conversion capability, and ketones from secondary alcohols where only a partial conversion is possible thanks to the structural limits.

Alcohols and Ketones

Alcohols are organic compounds containing one or more hydroxyl (-OH) groups attached to a carbon atom. They can be classified as primary, secondary, or tertiary, depending on the number of carbon atoms connected to the carbon with the -OH group.

In the reactions described, propan-1-ol is a primary alcohol and propan-2-ol is a secondary alcohol. Primary alcohols can be oxidized to carboxylic acids, while secondary alcohols typically form ketones. Ketones are compounds where a carbonyl group (C=O) is bonded to two carbon atoms, distinguishing these structures from other carbonyl-containing compounds like aldehydes and acids.

During the exercise, propan-1-ol was oxidized to propanoic acid, while propan-2-ol was oxidized to propanone (a ketone), showcasing the different reactions alcohols can undergo dependent on their classification.