Problem 46 - Chemistry and Chemical Reactivity

Question

Aldehydes and carboxylic acids are formed by oxidation of primary alcohols, and ketones are formed when secondary alcohols are oxidized. Give the name and formula for the alcohol that, when oxidized, gives the following products: (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH} \mathrm{O}\) (b) 2 -hexanone

Step-by-Step Solution

Answer

(a) Butan-1-ol: \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2}\mathrm{OH} \) (b) Hexan-2-ol: \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}(\mathrm{OH})\mathrm{CH}_{3} \)

Step 1: Understand the problem

We need to identify the primary alcohol corresponding to the aldehyde product and the secondary alcohol corresponding to the ketone product.

Step 2: Analyze product (a)

The product is \ \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH} \mathrm{O} \), which is an aldehyde named butanal. This aldehyde is formed from the oxidation of a primary alcohol with the same number of carbon atoms.

Step 3: Identify the alcohol for product (a)

Aldehydes are formed by the oxidation of primary alcohols; therefore, the alcohol is butan-1-ol, with the formula \ \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2}\mathrm{OH} \).

Step 4: Analyze product (b)

The product is 2-hexanone, a ketone. Ketones are formed when secondary alcohols are oxidized.

Step 5: Identify the alcohol for product (b)

The ketone 2-hexanone is formed from the oxidation of secondary alcohols; thus, the corresponding alcohol is hexan-2-ol, with the formula \ \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}(\mathrm{OH})\mathrm{CH}_{3} \).

Key Concepts

Aldehydes

Aldehydes are organic compounds that contain a carbonyl group (a carbon double-bonded to oxygen), where the carbon atom is also bonded to at least one hydrogen atom. This functional group gives aldehydes their distinct properties and reactivity. They are often recognized by their common suffix "-al" in the IUPAC naming system. A prime example is butanal with the formula \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH} \mathrm{O} \).
Aldehydes are typically formed through the oxidation of primary alcohols. The process involves removing hydrogen from the alcohol to form the carbonyl group. Notably, during this transformation, the carbon chain remains unchanged except for the new oxygen double bond.
Understanding the structure of aldehydes helps predict their chemical behavior. They often undergo further reactions such as hydrogeneration or can be converted into carboxylic acids through further oxidation.

Ketones

Ketones are characterized by a carbonyl group attached to two alkyl groups. Unlike aldehydes, the carbonyl carbon in ketones is not bonded to any hydrogen atoms. Their nomenclature often ends with "-one". An example of a ketone from the exercise is 2-hexanone, which has the structure \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{C(O)} \mathrm{CH}_{3} \).
Ketones are formed when secondary alcohols undergo oxidation, where the alcohol's hydroxyl group is converted into a carbonyl group without changing the carbon skeleton.
Ketones are generally more resistant to oxidation compared to aldehydes, meaning they do not easily convert into another oxidation product like acids. This stability is often leveraged in chemical industries where ketones are used as solvents and chemical precursors.

Primary Alcohols

Primary alcohols are a type of alcohol where the hydroxyl group (-OH) is connected to a carbon atom, which is attached to only one other alkyl group. They are represented as RCH\(_2\)OH where R is a hydrocarbon chain. An example given is butan-1-ol with the structure \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH} \).
Upon oxidation, primary alcohols commonly transform into aldehydes. This oxidation process involves the removal of two hydrogen atoms: one from the hydroxyl group and another from the carbon atom bonded to it. The result is the creation of a carbonyl group, turning the primary alcohol into an aldehyde.
Primary alcohols can undergo further oxidation to yield carboxylic acids if the reaction conditions permit, making them versatile in organic synthesis.

Secondary Alcohols

Secondary alcohols differ from primary alcohols in that their hydroxyl group (-OH) is attached to a carbon atom, which is connected to two other alkyl groups. This structural orientation makes them more stable than primary alcohols in terms of oxidation. A secondary alcohol in our example is hexan-2-ol, described with the formula \( \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}( ext{OH})\mathrm{CH}_{3} \).
When secondary alcohols undergo oxidation, the hydroxyl group's hydrogen and a hydrogen atom from the carbon are removed. This creates a carbonyl group, converting the alcohol into a ketone like 2-hexanone. Unlike primary alcohols, further oxidation does not proceed easily to carboxylic acids.
Due to their stability and specific reactivity patterns, secondary alcohols are significant in chemical manufacturing and synthesis processes, providing a pathway to create ketones and other valuable chemical compounds.