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9.5 - Physical Properties

Interactive Audio Lesson

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States of Amines

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Teacher
Teacher

Welcome class! Today we’ll be discussing the physical properties of amines. To start off, can anyone tell me what states lower aliphatic amines are typically found in?

Student 1
Student 1

Are they gases?

Teacher
Teacher

Exactly! Lower aliphatic amines are indeed gases with distinct fishy odors. What happens when we increase the number of carbon atoms in amines?

Student 2
Student 2

They can become liquids or even solids?

Teacher
Teacher

Correct! Primary amines with three or more carbon atoms become liquids, and higher ones typically are solid. This change in state relates to their structure and interactions. Let's remember this with the mnemonic 'Gas, Liquid, Solid—Amines Grow Up'—it's a good way to recall the progression.

Student 3
Student 3

What about aromatic amines like aniline?

Teacher
Teacher

Great question! Aniline and other arylamines are usually colorless but can oxidize and change color over time due to atmospheric interactions. It’s important to note that their chemical structure impacts these physical properties.

Solubility of Amines

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Teacher
Teacher

Now, let's dive into solubility. Who can explain why lower aliphatic amines are soluble in water?

Student 2
Student 2

They can form hydrogen bonds?

Teacher
Teacher

Exactly! The ability of amines to engage in hydrogen bonding with water molecules is key to their solubility. However, as the size of the alkyl part increases, solubility decreases. Can someone hypothesize why?

Student 1
Student 1

Because the hydrophobic character of the larger alkyl group outweighs the hydrogen bonding ability?

Teacher
Teacher

Exactly. This manifests in lower solubility as the hydrophobic portion grows. Now, comparing amines with alcohols, can anyone tell me which would generally be more soluble?

Student 4
Student 4

Alcohols, because they form stronger hydrogen bonds?

Teacher
Teacher

Correct! Alcohols are indeed more polar and can form stronger hydrogen bonds than amines. Let's remember that as a comparative relationship!

Boiling Points of Amines

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Teacher
Teacher

Next, let’s look at the boiling points of amines. How would you rank the boiling points of primary, secondary, and tertiary amines?

Student 3
Student 3

I think primary amines have the highest boiling points, right?

Teacher
Teacher

Exactly! Primary amines have the highest due to stronger intermolecular hydrogen bonding. Secondary amines are next, followed by tertiary amines, which do not participate in hydrogen bonding as effectively. Why do you think that is?

Student 2
Student 2

Because tertiary amines don’t have hydrogen atoms available for bonding?

Teacher
Teacher

Yes! The absence of hydrogen atoms in tertiary amines reduces their ability to form stronger intermolecular associations. Remember this ranking as 'Primary > Secondary > Tertiary' for boiling points.

Student 4
Student 4

So, that explains why aliphatic amines have different physical properties than alcohols!

Teacher
Teacher

Exactly! Those differences are pivotal in understanding their behavior in chemical reactions.

Introduction & Overview

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Quick Overview

This section discusses the physical properties of amines, including their state, solubility, and boiling points compared to alcohols and alkanes.

Standard

Amines possess distinct physical properties that stem from their molecular structure and hydrogen bonding capabilities. The section highlights that lower aliphatic amines are gaseous and soluble in water, while larger amines tend to be less soluble. Additionally, boiling points of amines are compared to alcohols and alkanes, emphasizing the role of hydrogen bonding in these differences.

Detailed

In this section, the physical properties of amines are explored in detail. Amines, generally considered derivatives of ammonia, exhibit various states based on molecular size—lower aliphatic amines are gases with notable fishy odors, while primary amines with three or more carbons are liquids, and still higher amines are solids. Aniline, along with other arylamines, typically appears colorless but can oxidize upon storage, impacting its color.

Amines are soluble in water due to their ability to form hydrogen bonds, although solubility decreases with increasing molecular weight as the hydrophobic character of the alkyl group prevails. The section contrasts the solubility of amines with that of alcohols, highlighting that alcohols form stronger hydrogen bonds and are thus more polar. The relationship between intermolecular association, particularly through hydrogen bonds, further explains the boiling point differences among primary, secondary, and tertiary amines, where primary amines have the highest boiling points due to stronger intermolecular associations.

This understanding of physical properties sets the foundation for exploring the chemical reactions and uses of amines, helping to elucidate their behavior in various chemical contexts.

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Audio Book

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Physical State of Amines

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The lower aliphatic amines are gases with fishy odour. Primary amines with three or more carbon atoms are liquid and still higher ones are solid. Aniline and other arylamines are usually colourless but get coloured on storage due to atmospheric oxidation.

Detailed Explanation

Amines vary in physical state based on their molecular structure and size. Lower aliphatic amines, those with fewer carbons, are typically gases and often have a distinct fishy smell. As the number of carbon atoms increases, primary amines transition from gaseous to liquid states and finally to solids as more complex structures form. Aniline, a commonly studied arylamine, is initially colorless, but it can take on color when exposed to air over time, indicating oxidation.

Examples & Analogies

Think of amines like perfumes that evolve as the ingredients change. Just like some smells are stronger or more noticeable in solid forms than in gases, the physical state of amines influences not just how they smell but also how we interact with them.

Solubility of Amines

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Lower aliphatic amines are soluble in water because they can form hydrogen bonds with water molecules. However, solubility decreases with increase in molar mass of amines due to increase in size of the hydrophobic alkyl part.

Detailed Explanation

Amines can dissolve in water because of their ability to form hydrogen bonds, which are attractive forces between molecules. Lower molecular weight amines, due to their smaller alkyl groups, are more capable of interacting with water molecules effectively. However, as the size of the alkyl group increases, the hydrophobic (water-repelling) region of the amines outweighs their ability to bond with water, resulting in lower solubility. This illustrates the balance between hydrophilic (water-attracting) and hydrophobic properties within molecules.

Examples & Analogies

Consider sugar versus oil in water. Sugar dissolves easily because it forms strong interactions with water, akin to how lower amines behave. In contrast, oil does not mix well because its molecules are larger and cannot form similar binding interactions, much like how larger amines show lower solubility.

Comparison of Solubility and Boiling Points

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Amines are soluble in organic solvents like alcohol, ether and benzene. You may remember that alcohols are more polar than amines and form stronger intermolecular hydrogen bonds than amines.

Detailed Explanation

Amines can dissolve in various organic solvents due to their structure; however, they are generally less polar than alcohols. Alcohols, having hydroxyl groups (-OH), create stronger hydrogen bonds compared to the amino groups (-NH2) found in amines. This means that while amines can dissolve in organic solvents, they may not interact as effectively as alcohols, which leads to differences in solubility.

Examples & Analogies

Think of alcohol being the life of the party (as it's very social) compared to amines who might participate but are not as engaging. Alcohols draw in water (and other polar molecules) more effectively due to their strong hydrogen bonds, like a friendly person who bonds easily with everyone.

Boiling Points Related to Hydrogen Bonding

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Primary and secondary amines are engaged in intermolecular association due to hydrogen bonding between nitrogen of one and hydrogen of another molecule. This intermolecular association is more in primary amines than in secondary amines as there are two hydrogen atoms available for hydrogen bond formation in it.

Detailed Explanation

The boiling points of amines are influenced by their ability to form hydrogen bonds with each other. Primary amines can form more hydrogen bonds since they have two hydrogen atoms available for bonding, compared to secondary amines, which have only one. This leads to stronger intermolecular forces in primary amines, resulting in higher boiling points. Tertiary amines, lacking hydrogen atoms on nitrogen, cannot form these bonds, leading to the lowest boiling points among the three types of amines.

Examples & Analogies

Imagine building a tower. The more connections (or bonds) you can make with others, the taller your tower can stand. Primary amines can connect more effectively, creating a tall tower (high boiling point), while tertiary amines are like a small platform\u2014stable but not high because they can\u2019t connect as many.

Comparative Boiling Points of Amines, Alcohols, and Alkanes

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Boiling points of amines, alcohols and alkanes of almost the same molar mass are shown in Table 9.2.

Detailed Explanation

When comparing boiling points, primary amines generally have higher boiling points than tertiary amines, alkanes, and alcohols of similar molar mass. Alcohols have higher boiling points than amines due to stronger hydrogen bonding. While alkanes are the least affected by hydrogen bonding, they experience only van der Waals forces which lead to much lower boiling points. This illustrates how molecular structure and interaction types govern the physical properties of substances.

Examples & Analogies

Think about how the waters in a pot boil: stronger connections (like hydrogen bonds in alcohols) mean the water needs more energy (heat) to break those connections and boil compared to weaker connections (like in alkanes), which might boil away quickly at lower temperatures.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • States of Amines: Lower aliphatic amines are gases, while higher amines are liquids or solids.

  • Solubility: Amines' ability to form hydrogen bonds enables their solubility in water, decreasing with larger alkyl groups.

  • Boiling Points: The boiling point order is primary > secondary > tertiary due to hydrogen bonding strength.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • Trimethylamine is a gas, while heptanamine is a liquid and hexadecylamine is a solid.

  • Butanamine (a primary amine) has a higher boiling point than N,N-dimethylamine (a tertiary amine).

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎵 Rhymes Time

  • Amines gas, with odors that pass, liquids and solids for those with more mass.

📖 Fascinating Stories

  • Imagine a party where lower aliphatic amines dance around as gaseous hosts, but as more guests arrive with bigger sizes, they turn into liquids and solids, holding their ground.

🧠 Other Memory Gems

  • Remember 'PST' for boiling points: Primary, Secondary, Tertiary – the order of heights they can be when they boil!

🎯 Super Acronyms

Use 'SAG'

  • Solubility (amides can bond)
  • Amount of carbon increasing lowers solubility
  • Gases for lower amines.

Flash Cards

Review key concepts with flashcards.

Glossary of Terms

Review the Definitions for terms.

  • Term: Amines

    Definition:

    Organic compounds derived from ammonia by replacing one or more hydrogen atoms with alkyl or aryl groups.

  • Term: Hydrogen Bonding

    Definition:

    A strong type of intermolecular force that occurs between molecules with hydrogen attached to electronegative atoms.

  • Term: Solubility

    Definition:

    The ability of a substance to dissolve in a solvent.

  • Term: Aliphatic Amines

    Definition:

    Amines that contain straight or branched-chain hydrocarbons.

  • Term: Aryl Amines

    Definition:

    Amines where the amino group is attached directly to an aromatic ring.