Kuliah Online Kimia Organik 2 S1 Kimia IPB: Amina Bagian 2 - Sifat Amina

Summary

This video discusses the chemical properties of amines, including their ability to form hydrogen bonds, their boiling points, and their basicity. It explains how amines can react with acids to form ammonium salts and compares the basicity of primary, secondary, and tertiary amines. The script also touches on the differences between amines and amides, as well as the influence of substituents on the basicity of aromatic and aliphatic amines. Practical examples of separating amines from mixtures and their reactions with strong bases are also covered.

Takeaways

• 😀 Amines typically form three bonds and leave one lone pair of electrons, creating a trigonal pyramidal geometry.
• 😀 Amines can be chiral if the three substituents on the nitrogen are different, but they often exist as racemates due to fast inversion of the pyramid.
• 😀 Amines can form hydrogen bonds with water and other amines, making them soluble in water and giving them higher boiling points compared to alkanes.
• 😀 The boiling point of amines is higher than alkanes because amines can form stronger hydrogen bonds, while alkanes only have London dispersion forces.
• 😀 Alcohols have higher boiling points than amines because their hydrogen bonding is stronger due to the higher electronegativity of oxygen compared to nitrogen.
• 😀 The boiling point of amines increases with molecular weight (larger alkyl groups), but tertiary amines have lower boiling points than secondary and primary amines due to the lack of hydrogen bonding.
• 😀 Amines are basic according to Lewis theory, and they can react with acids to form ammonium salts.
• 😀 The basicity of amines can be measured using the KB constant, where higher KB values indicate stronger basicity and smaller PKB values.
• 😀 Secondary amines are the most basic, as they can form stable ammonium ions by hydrogen bonding, unlike tertiary amines which lack hydrogen for hydrogen bonding.
• 😀 Amides are less basic than amines because the nitrogen in amides is less electron-rich due to resonance with the adjacent carbonyl group, reducing its ability to accept protons.

Q & A

What geometric shape does Aminah form when bonding with three different substituents?

Aminah forms a trigonal pyramidal shape when it bonds with three different substituents, leaving one lone pair of electrons (PEB) on the nitrogen atom.

How does the ability to form hydrogen bonds affect the boiling point of Aminah?

The ability of Aminah to form hydrogen bonds significantly increases its boiling point. This is because hydrogen bonds are stronger interactions compared to London dispersion forces, which are present in alkanes.

Why does the boiling point of Aminah differ from alcohol, even though both can form hydrogen bonds?

The hydrogen bonds in Aminah are not as strong as those in alcohol due to the lower electronegativity of nitrogen compared to oxygen. As a result, alcohols have higher boiling points than Aminah.

Why does ethylamine have a higher boiling point than methylamine?

Ethylamine has a higher boiling point than methylamine because it has a larger molecular weight (bigger molecular mass), which results in more intermolecular interactions and a higher boiling point.

Why does trimethylamine have a lower boiling point than dimethylamine despite having a higher molecular weight?

Trimethylamine has a lower boiling point than dimethylamine because it is a tertiary amine and lacks a hydrogen atom on the nitrogen, meaning it cannot form hydrogen bonds between molecules, which lowers its boiling point.

How does the basicity of Aminah relate to its ability to accept protons?

Aminah is basic because the nitrogen atom has a lone pair of electrons (PEB), which it can donate to accept protons. The more electron-rich the nitrogen, the stronger the base, and the easier it is to form ammonium salts.

What is the relationship between the value of PKB and the basicity of Aminah?

A lower PKB value corresponds to a stronger base because it indicates a higher equilibrium constant for protonation. Therefore, Aminah with a lower PKB value is more basic.

Why is secondary Aminah typically more basic than primary or tertiary Aminah?

Secondary Aminah is more basic than primary or tertiary Aminah because it has two alkyl groups that donate electron density to the nitrogen, making it more electron-rich and more likely to accept protons.

What effect does a carbonyl group have on the basicity of an amide compared to Aminah?

The carbonyl group in amides pulls electron density away from the nitrogen via induction and resonance, which makes the nitrogen less electron-rich and less basic compared to Aminah.

How do substituents affect the basicity of aromatic amino compounds?

Substituents on an aromatic amino compound can either donate or withdraw electron density from the nitrogen. Electron-donating groups (such as alkyl or ether groups) make the compound more basic, while electron-withdrawing groups (such as halogens or nitro groups) make it less basic.