Problem 52 - Chemistry and Chemical Reactivity

Question

Give the structural formula and name for the organic product from the following reactions. (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CHO}+\mathrm{LiAlH}_{4}\) (b) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{OH}+\mathrm{KMnO}_{4}\)

Step-by-Step Solution

Answer

(a) 1-Butanol (CH₃CH₂CH₂CH₂OH). (b) Butanoic acid (CH₃CH₂CH₂COOH).

Step 1: Understand the Reagents and Initial Compounds (Reaction a)

The initial compound is butanal (CH₃CH₂CH₂CHO), an aldehyde. The reagent is LiAlH₄ (lithium aluminum hydride), a strong reducing agent.

Step 2: Determine the Reduction Product (Reaction a)

LiAlH₄ reduces aldehydes to primary alcohols. Therefore, butanal will be reduced to butanol, specifically 1-butanol or n-butanol.

Step 3: Draw the Structural Formula (Reaction a)

The structural formula for 1-butanol is CH₃CH₂CH₂CH₂OH. The aldehyde group is replaced by a hydroxyl group when reduced by LiAlH₄.

Step 4: Understand the Reagents and Initial Compounds (Reaction b)

The initial compound is 1-butanol (CH₃CH₂CH₂CH₂OH), a primary alcohol. The reagent is KMnO₄, a strong oxidizing agent often used in acidic or basic solutions.

Step 5: Determine the Oxidation Product (Reaction b)

KMnO₄ will oxidize the primary alcohol to a carboxylic acid. Therefore, 1-butanol will be oxidized to butanoic acid.

Step 6: Draw the Structural Formula (Reaction b)

The structural formula for butanoic acid is CH₃CH₂CH₂COOH. The primary alcohol group is oxidized to a carboxylic acid group.

Key Concepts

Aldehydes to Alcohols Reduction

Reducing aldehydes to alcohols is a common reaction in organic chemistry that involves the addition of hydrogen to a carbonyl group. A popular reagent for this transformation is Lithium aluminum hydride (LiAlH₄), which is a very strong reducing agent.
When an aldehyde like butanal (CH₃CH₂CH₂CHO) is treated with LiAlH₄, the aldehyde's carbonyl group (C=O) undergoes reduction. This process converts the double-bonded oxygen into a hydroxyl group (OH), turning the aldehyde into a primary alcohol like 1-butanol (CH₃CH₂CH₂CH₂OH).
Here's how it works:

• The aldehyde molecule interacts with LiAlH₄, which donates hydride ions (H⁻).
• A hydride ion attacks the carbonyl carbon, breaking the double bond and forming a new bond with the oxygen.
• This results in an alcohol, as the oxygen in the original carbonyl group now holds an extra hydrogen, becoming an OH group.

Understanding this reduction reaction is crucial because it often serves as a step in the synthesis of more complex organic compounds.

Oxidation of Alcohols

The oxidation of alcohols is another fundamental reaction in organic chemistry. It involves increasing the oxidation state of the alcohol's carbon, typically converting it into a carbonyl compound.
A common oxidizing agent used for primary alcohols like 1-butanol (CH₃CH₂CH₂CH₂OH) is potassium permanganate (KMnO₄). KMnO₄ will oxidize 1-butanol to butanoic acid (CH₃CH₂CH₂COOH), a primary alcohol to a carboxylic acid conversion.

• Initially, the primary alcohol's hydroxyl group undergoes oxidation, increasing the oxidation state.
• The oxidation converts the alcohol group into a carboxylic acid group by formulating a C=O (carbonyl) group and an OH (hydroxyl) group attached to the same carbon, forming the COOH structure.
• This oxidation reaction is essential in organic synthesis, as it helps create carboxylic acids, which are vital building blocks in numerous chemical processes.

Recognizing the role of oxidation in transforming alcohols into acids provides insights into the broader scope of chemical reactions and pathways.

Structural Formulas

Structural formulas are crucial representations in organic chemistry that depict the arrangement of atoms within a molecule. They help chemists visualize and understand how atoms are connected, which in turn influences the properties and reactions of the molecules.
For instance, taking the molecule 1-butanol with the structural formula CH₃CH₂CH₂CH₂OH, shows:

• Four carbon atoms in a straight chain, illustrating its primary alcohol structure.
• Attached to the terminal carbon is a hydroxyl group (OH), signifying its alcohol functional group.

When considering the oxidation product butanoic acid, with the formula CH₃CH₂CH₂COOH:

• The same linear chain of carbon atoms is seen, as in 1-butanol.
• However, the oxidation converts the terminal alcohol group into a carboxylic acid group (COOH).
• This subtle yet significant change is easily visualized through the structural formula, highlighting the impact of chemical reactions on molecular structure.

Structural formulas thus serve as a visual map for chemists, detailing important aspects of molecular architecture that might not be immediately apparent from a molecule's empirical or molecular formula alone.