Carboxylic acid introduction | Carboxylic acids and derivatives | Organic chemistry | Khan Academy

Summary

This script explores carboxylic acids, highlighting their structure with a carbonyl group and an OH group. It explains their acidity through resonance stabilization and the formation of carboxylate ions. Common examples like acetic acid, formic acid, and oxalic acid are introduced, emphasizing their naming patterns and properties.

Takeaways

• 🔍 Carboxylic acids have a carbonyl group attached to a hydroxyl group, differing from aldehydes and ketones by the presence of the OH group.
• 🍋 Carboxylic acids are more acidic than alcohols due to their ability to donate a proton and form a resonance-stabilized carboxylate ion.
• 🧲 The oxygen in the carbonyl group can pull the electron from the hydrogen in the hydroxyl group, facilitating the release of a proton.
• 🌊 When carboxylic acids are in water, they donate a proton to a water molecule, forming a hydronium ion and a carboxylate ion.
• 🔋 The carboxylate ion is stabilized by resonance, which involves the delocalization of electrons across the molecule.
• 📚 The resonance stabilization of the carboxylate ion makes carboxylic acids stronger acids compared to alcohols.
• 📘 The presence of an electronegative R group can further stabilize the carboxylate ion, enhancing the acidity of the carboxylic acid.
• 🧪 Common carboxylic acids include acetic acid, which has a one-carbon chain, and formic acid, which is even simpler.
• 🔗 Oxalic acid is a unique carboxylic acid with two carboxyl groups that can be deprotonated twice.
• 📝 Carboxylic acids are systematically named based on the length of the carbon chain and the position of the carboxyl group.
• 📚 Memorizing common carboxylic acids like acetic, formic, and oxalic acids can be facilitated by recognizing their structural similarities and prefixes.

Q & A

What is the general form of a carboxylic acid?

A carboxylic acid has the general form of a carbonyl group attached to a hydroxyl (OH) group as part of a longer carbon chain. Unlike aldehydes, which have a hydrogen atom, or ketones, which have another carbon chain, the OH group is present in carboxylic acids.

Why are carboxylic acids considered to be acidic?

Carboxylic acids are considered acidic because they can donate a proton (H+). This is due to the ability of the oxygen atom in the OH group to take the electron from the hydrogen atom, thus releasing the proton.

How does the loss of a hydrogen atom in a carboxylic acid lead to the formation of a carboxylate ion?

When a carboxylic acid loses its hydrogen atom, the oxygen atom takes back the electron from the hydrogen, which results in the formation of a carboxylate ion. The carboxylate ion is more stable due to resonance stabilization.

What is the role of resonance stabilization in the carboxylate ion?

Resonance stabilization in the carboxylate ion allows the negative charge to be delocalized across the molecule, making it more stable than the conjugate base of an alcohol. This stabilization occurs through the sharing of the extra electron between the oxygen and carbon atoms.

How does the presence of an electronegative R group affect the acidity of a carboxylic acid?

An electronegative R group can withdraw electrons from the carboxylate ion, which further stabilizes the ion and makes the carboxylic acid a stronger acid. This is because the electronegative group can attract the negative charge, enhancing the stability of the conjugate base.

What is the conjugate base of a carboxylic acid?

The conjugate base of a carboxylic acid is the carboxylate ion, which is formed when the carboxylic acid donates a proton (H+).

What is the difference between a carboxylic acid and an alcohol in terms of acidity?

Carboxylic acids are more acidic than alcohols because the carboxylate ion formed after the loss of a proton is resonance stabilized, making it a stronger base and thus the carboxylic acid a stronger acid.

What is the systematic name for the carboxylic acid with a single carbon chain?

The systematic name for the carboxylic acid with a single carbon chain is formic acid.

What is acetic acid, and how is it named?

Acetic acid is a carboxylic acid with a single methyl group attached to the carbonyl group. It is named by taking the prefix 'acetic' from the simpler aldehyde and ketone with the same carbon chain, acetaldehyde and acetone, respectively.

What is oxalic acid, and how does its structure differ from other carboxylic acids?

Oxalic acid is a dicarboxylic acid with two carboxyl groups attached to each other. It can be deprotonated twice, which is different from most carboxylic acids that typically have only one carboxyl group.

What is the significance of the hydronium ion in the context of carboxylic acid dissociation?

The hydronium ion (H3O+) is significant because it is the product of water donating a proton to the carboxylate ion. This increases the concentration of protons in the solution, which is a measure of acidity.