Hydrocarbon Power!: Crash Course Chemistry #40

Summary

This script delves into the significance of carbon in organic chemistry, highlighting its versatility in forming various molecular structures. It introduces alkanes as the simplest hydrocarbons, explaining their naming conventions, isomers, and common uses. The episode also covers three key reactions of alkanes: combustion, halogenation, and dehydrogenation, providing foundational knowledge for further exploration into organic chemistry.

Takeaways

• 🌿 Carbon is the key element in organic compounds and is essential for life, prompting its search in the exploration of other planets for signs of life.
• 🧪 The term 'organic' originated from the belief that such compounds could only be produced by living organisms, until Friedrich Wöhler synthesized urea from an inorganic compound in 1828.
• 🔬 Carbon's versatility in forming a variety of structures is due to its four valence electrons which can bond with other atoms in numerous configurations.
• 🔋 Hydrocarbons, the simplest organic molecules composed of carbon and hydrogen, are the foundation of biological molecules and are crucial in organic chemistry.
• 🚗 Saturated hydrocarbons, known as alkanes, are the basis for fuels like diesel, gasoline, methane, and propane, which are vital for various aspects of modern life.
• 🔍 Alkanes are named based on the longest continuous chain of carbon atoms, with prefixes indicating the number of carbons and numbers for the position of branches.
• 🔄 Isomers are compounds with the same molecular formula but different structural arrangements, leading to different physical properties, such as boiling points.
• 📚 The naming system for organic compounds, including alkanes, is systematic, involving prefixes for the number of carbons and suffixes for the type of compound.
• 🔥 Combustion is a major reaction type for alkanes, producing carbon dioxide and water vapor, and is the chemical process behind engines and burning fuels.
• 🧩 Halogenation involves the substitution of hydrogen atoms in alkanes with halogen atoms, creating new compounds like chloroform from methane and chlorine.
• 🌐 Dehydrogenation is the removal of hydrogen atoms from alkanes, resulting in the formation of double or triple bonds and creating unsaturated hydrocarbons with different properties.

Q & A

Why is carbon considered the element of life?

Carbon is considered the element of life because it forms the basis of most biological molecules. It is in group 14 on the periodic table and has 4 valence electrons that can bond to other atoms in various configurations, allowing it to form complex structures essential for life.

What was the significance of Friedrich Wöhler's discovery in 1828?

Friedrich Wöhler's discovery in 1828 was significant because he synthesized urea, a biological molecule, from ammonium cyanate, an inorganic compound. This proved that biological molecules could be created artificially, not just produced by living organisms, and marked the birth of organic chemistry.

What are hydrocarbons and why are they important in organic chemistry?

Hydrocarbons are organic compounds containing only carbon and hydrogen. They are important in organic chemistry because they are the simplest organic molecules and follow straightforward rules, making them a good starting point for understanding more complex organic compounds.

What is the difference between alkanes and other hydrocarbons?

Alkanes are a type of hydrocarbon where all the carbons are bound to the maximum number of atoms (four each) without any double or triple bonds, making them fully saturated. Other hydrocarbons, such as alkenes and alkynes, contain double or triple bonds and have different properties and reactions.

What is an isomer and why are they significant in chemistry?

Isomers are compounds that have the same molecular formula but different structural arrangements. They are significant in chemistry because different structures can lead to different properties, even though the compounds have the same chemical composition.

How do the properties of alkanes change as the number of carbon atoms increases?

As the number of carbon atoms in alkanes increases, their molecules can pack more densely together. This typically results in a change of state from gaseous at smaller chain lengths to liquid or solid at larger chain lengths at room temperature.

What is the general process of naming alkanes in organic chemistry?

Alkanes are named based on the longest continuous chain of carbon atoms present in their structure, using prefixes to indicate the number of carbon atoms. Branches or side chains are indicated by numbers showing their position on the main chain and are named with a -yl suffix. The main chain is numbered to give the lowest possible numbers to the branches.

What are the three major types of reactions that alkanes can undergo?

The three major types of reactions that alkanes can undergo are combustion, where they react with oxygen to produce carbon dioxide and water; halogenation, where hydrogen atoms are replaced by halogen atoms; and dehydrogenation, where hydrogen atoms are removed, leading to the formation of double or triple bonds.

Why is the term 'combustion' often misunderstood to mean 'explosion'?

Combustion is often misunderstood to mean 'explosion' because both involve the rapid release of energy. However, combustion is a specific type of chemical reaction that involves a hydrocarbon and oxygen, producing carbon dioxide and water, and does not necessarily result in an explosion.

How can one build a structural formula of an alkane from its name?

To build a structural formula from an alkane's name, start with the main chain indicated by the prefix, then add any substituent groups (like methyl or ethyl groups) at the carbon positions indicated by the numbers. Finally, add hydrogen atoms to ensure that each carbon atom has four bonds.

What is the role of the prefixes in organic nomenclature?

Prefixes in organic nomenclature indicate the number of carbon atoms in a molecule or a substituent group. For example, 'meth-' indicates one carbon atom, 'eth-' indicates two, 'prop-' indicates three, and 'but-' indicates four.

Outlines

00:00

🌿 The Essence of Organic Chemistry: Carbon and Hydrocarbons

This paragraph delves into the fundamental role of carbon as the cornerstone of life and organic chemistry. It explains how carbon's unique ability to form a variety of bonds with four valence electrons makes it essential for biological molecules. The narrative begins with a historical perspective on organic compounds and their synthesis by Friedrich Wöhler in 1828, debunking the myth that they could only be produced by living organisms. It then introduces the concept of hydrocarbons, the simplest organic molecules composed of carbon and hydrogen, and explains the structure of alkanes, the fully saturated hydrocarbons. The paragraph also touches on the naming conventions for alkanes, such as methane, ethane, and propane, and their various applications, including as fuels and in the production of plastics. The introduction of isomers, compounds with the same molecular formula but different structural arrangements, is highlighted, with examples like n-butane and isobutane, which have distinct properties despite identical chemical formulas.

05:02

🔍 Organic Nomenclature and the Structure of Alkanes

This paragraph provides an in-depth look at the naming system for organic compounds, specifically alkanes. It explains the significance of prefixes in denoting the number of carbon atoms in a molecule and how these prefixes are used to identify various groups within the molecule, such as methyl and ethyl. The paragraph outlines the rules for naming alkanes, emphasizing the importance of identifying the longest continuous chain and numbering it to give the lowest possible numbers to the attached groups. It also addresses the concept of isomers, using isobutane as an example to illustrate how different arrangements of carbon atoms can lead to different compounds with distinct properties. The summary further explores the process of naming complex alkanes with multiple attachments and demonstrates how to construct an alkane structure from its name, emphasizing the utility of this knowledge in understanding and predicting the behavior of organic compounds in various reactions.

10:04

🔥 Reactions of Alkanes: Combustion, Halogenation, and Dehydrogenation

The final paragraph of the script focuses on the chemical reactions that alkanes can undergo. It clarifies the common misconception that combustion is synonymous with explosion, explaining that combustion is a controlled reaction that powers many of our daily technologies, such as cars and grills. The paragraph details the process of combustion, where hydrocarbons react with oxygen to produce carbon dioxide and water vapor. It also discusses halogenation, a reaction where hydrogen atoms in alkanes are replaced by halogen atoms, exemplified by the formation of trichloromethane from methane and chlorine gas. Lastly, dehydrogenation is introduced as a reaction that removes hydrogen atoms from alkanes, leading to the formation of double or triple bonds and the creation of unsaturated hydrocarbons. The paragraph concludes by summarizing the key points covered in the video, including the classification of organic compounds, the structure and properties of alkanes, the importance of isomers, the process of naming and constructing alkane structures, and the types of reactions alkanes can experience.

Keywords

💡Carbon

Carbon is a chemical element with the symbol C and atomic number 6. It is the fundamental element of life, as it forms the backbone of all biological molecules. In the script, carbon's importance is highlighted by its presence in compounds that are essential for life and its role in the formation of organic compounds. The video discusses how carbon's ability to form a variety of structures makes it the foundation of most biological molecules.

💡Organic Compounds

Organic compounds are chemical compounds that contain carbon, often bonded to hydrogen, oxygen, and other elements. They are the basis of life and are the focus of the script's discussion. The term originated from the belief that such compounds could only be produced by living organisms, but this was disproved by Friedrich Wöhler's synthesis of urea from an inorganic compound.

💡Friedrich Wöhler

Friedrich Wöhler was a German chemist who is known for his role in the history of organic chemistry. His synthesis of urea from inorganic materials demonstrated that organic compounds could be created artificially, which was a significant breakthrough in the field. The script mentions his experiment as the birth of organic chemistry.

💡Hydrocarbons

Hydrocarbons are organic compounds consisting only of hydrogen and carbon atoms. They are the simplest type of organic compounds and are the starting point of the video's exploration of organic chemistry. Examples given in the script include methane, ethane, and propane, which are foundational to understanding the properties and reactions of more complex organic molecules.

💡Alkanes

Alkanes are a class of hydrocarbons that are fully saturated, meaning that their carbon atoms are bonded to the maximum number of hydrogen atoms. They are named for their simplicity and are the focus of the script's discussion on the basic structures and properties of hydrocarbons. Examples such as methane (CH4) and ethane (C2H6) are used to illustrate the naming and structure of alkanes.

💡Isomers

Isomers are molecules with the same molecular formula but different structural arrangements of atoms. The script explains isomers in the context of butane, which has two isomers: n-butane and isobutane. The concept of isomers is crucial for understanding how different structures can lead to different properties, even with the same chemical formula.

💡Nomenclature

Nomenclature in chemistry refers to the systematic naming of chemical compounds. The script delves into the rules of organic nomenclature, particularly for alkanes, explaining how prefixes indicate the number of carbon atoms and how the position of substituents is denoted numerically. This is essential for both understanding and communicating about the structure of organic compounds.

💡Combustion

Combustion is a chemical reaction between a hydrocarbon and oxygen that produces carbon dioxide and water, releasing energy in the form of heat and light. The script clarifies that combustion is not synonymous with explosion and is the reaction that powers many alkane-based fuels, such as those in cars and propane grills.

💡Halogenation

Halogenation is a chemical reaction where halogen atoms replace hydrogen atoms in an alkane. The script uses the example of chloroform, which is correctly named trichloromethane, to illustrate this reaction. Halogenation is an important reaction type that modifies the properties of alkanes.

💡Dehydrogenation

Dehydrogenation is the chemical process where hydrogen atoms are removed from a molecule. In the context of the script, ethane can be dehydrogenated to form ethene, which involves the formation of a double bond between carbon atoms. This reaction is significant as it transforms saturated hydrocarbons into unsaturated ones.

Highlights

Carbon is the key element of life and is central to the search for life on other planets.

The term 'organic compounds' originated from the belief that they could only be produced by living organisms.

Friedrich Wöhler's synthesis of urea in 1828 disproved the vitalistic theory and marked the birth of organic chemistry.

Carbon's unique ability to form a variety of structures with its 4 valence electrons is crucial to its role in biology.

Hydrocarbons, the simplest organic molecules, are composed solely of carbon and hydrogen.

Saturated hydrocarbons, or alkanes, are fully bonded with no double or triple bonds, exemplified by methane and ethane.

Alkanes such as propane and butane are used in various applications, including as fuels and propellants.

Butane exhibits isomerism, with n-butane and isobutane having different structures and properties despite the same chemical formula.

The number of isomers increases exponentially with the number of carbon atoms in an alkane.

Larger and more complex alkanes tend to be liquid or solid at room temperature due to denser molecular packing.

Organic nomenclature uses a system of prefixes, suffixes, and numbers to convey the structure of compounds.

Alkane naming prioritizes the longest continuous chain and uses prefixes to indicate the number of carbon atoms.

Attachments to the main chain are named and numbered to indicate their position, as seen in 4-ethyloctane.

Isomers like isobutane are named based on the longest carbon chain and any attachments, as 2-methylpropane.

Multiple attachments are indicated with prefixes like di- and tri-, and listed alphabetically, as in 2,5-dimethyloctane.

Organic compound names can be reverse-engineered to construct their structural formulas, demonstrated with 2-ethyl-3,5-dimethylnonane.

Alkanes undergo combustion, halogenation, and dehydrogenation reactions, which are crucial for their applications.

Combustion of alkanes produces carbon dioxide and water vapor, a process distinct from explosion.

Halogenation involves the substitution of hydrogen atoms in alkanes with halogen atoms, as seen in trichloromethane.

Dehydrogenation removes hydrogen atoms from alkanes, leading to the formation of double or triple bonds.

Transcripts

You've heard this before, but it bears repeating. Carbon is the element of life.

So much so that when we explore other planets the first thing we look for is compounds that contain carbon.

In fact, there was a time when we thought carbon compounds could only be produced by living things.

So early chemists called them, as we still do today organic compounds.

Scientists back then considered biological molecules to be almost mystical in origin.

Until, 1828 when German chemist Friedrich Wöhler discovered that urea, a component of urine,

could be synthesized simply by heating ammonium cyanate, an inorganic compound.

That proved biological molecules were just chemicals that could be created and manipulated in the lab.

Suddenly a new branch of chemistry was born, organic chemistry. It's like my favorite chemistry.

So what is it about carbon though, that makes it so special? Well, a lot of things.

Like silicon, which we talked about a few weeks ago, carbon is in group 14 on the periodic table,

and like all of the elements in that group, it has 4 valence electrons.

In carbon those 4 electrons can bond to other atoms in a really promiscuous number of configurations

to form all kinds of structures.

Which is why carbon is to biology, which silicon is to geology.

Just as silicon forms the basis, not only for sand,

but also most of the rocks on earth, carbon is the foundation of most biological molecules.

Really all biological molecules...right? Yup.

The simplest organic molecules are pure hydrocarbons containing only carbon and hydrogen. Hydro-carbon.

They are where we're going to start our six week exploration of organic chemistry.

And they're a good place to start, partly because they play by the most straight forward rules.

When all carbons in a pure hydrocarbon are bound to the maximum number of atoms, 4 atoms each,

so that there are no double or triple bonds anywhere; these compounds are considered to be full or saturated.

That means that all the carbons have 4 bonds, either with other carbon atoms or with hydrogen atoms,

in which case the hydrogens are bound to one carbon.

No questions, no exceptions.

These are the simple rules that govern some of the world's most useful, or at least, used compounds.

The hydrocarbons that we use as diesel fuel, gasoline, methane, propane.

You're gonna learn what these and other compounds look like, what they're names mean,

and how they take part in the reactions that fuel our lives.

Welcome to organic chemistry!

[Theme Music]

The fully saturated hydrocarbons I just described are usually called by the much simpler name, alkanes.

The simplest of the alkanes is one you've heard of before, methane, or CH4, the main compound in natural gas.

The next simplest alkane contains 2 carbons side by side, each one of them in bonded to 3 hydrogen atoms.

This is ethane, C2H6. Another gas, and it's mostly used in the production of plastics.

If we add another carbon and enough hydrogens to fill all those spaces we get our next alkane:

propane, C3H8.

Also a gas at room temperature and normal atmospheric pressure,

propane is a common fuel for cooking, heating, and vehicles,

as well as a propellant for everything from aerosol cans to paintball guns.

And we could do this all day, adding carbons to the chain and giving each compound a name,

but that would be pretty boring.

Things get more interesting, though, with the next alkane, butane, C4H10,

because there are two different forms of it.

The first is what you'd expect:

just a chain of carbons with hydrogens stuck wherever they're needed to make each carbon have 4 bonds.

This is called normal butane or n-butane.

But you can also arrange the 4 carbons differently by making a chain of 3

and then branching the fourth one off the center of the chain.

This is called isobutane or i-butane.

And even though it has the same chemical formula as n-butane, its structure gives it different properties.

For example, n-butane boils at -0.5 degrees Celsius while isobutane boils at -11.7 degrees Celsius.

These different structures for compounds that have the same molecular formula are called isomers.

As you add more and more carbon atoms to the molecule, there are more and more ways that you can arrange them.

So the number of atoms is butane only allows for 2 isomers, n-butane and isobutane.

But pentane, C5H12, has 3 possible isomers and C6H14, known as hexane, has 5.

Again, I could do this all day.

But looking at this table of the number of possible isomers you could see that that escalated quickly.

The take away here is that molecules that have the same mass and number of atoms can form different structures.

And as their structure changes, their properties also change.

As a general rule, the larger and more complex alkanes are, the more densely their molecules can pack together,

which means that they tend to be liquid or solid instead of gaseous at room temperature.

So alkanes with 5 to 18 chains of carbon atoms like octane and gasoline are liquids at room temperature

and those with more than 18 carbon atoms like paraffin or other waxes are solids.

Now you're probably picking up on a lot of words that you've heard before, even outside of chemistry class:

octane, propane, methane, paraffin, and so on.

You can chalk that up to the enormous popularity of these compounds in our daily lives.

Like I said, hydrocarbons are super useful because of the types of reactions they can take part in,

which I will explain more in a bit.

But first, I think it's high time you know what these names actually mean.

Much like the general language of chemistry that we talked about months ago,

organic nomenclature has its own system of prefixes, suffixes, and numbers

that tell you what's in the compound being named.

Now you gotta know the prefixes because they indicate how many carbon atoms are present.

Here's one that I know you've heard before: meth.

Meth- in a name always indicates a molecule or branch containing one carbon atom.

So the difference between amphetamines doctors prescribe

and methamphetamines that are sold on the streets is that

methamphetamine has a methyl group, CH3 with one carbon,

where amphetamine just has a single hydrogen atom.

Hopefully, that's helpful to you. Don't do drugs.

Eth- in a name means 2carbon atoms.

Prop- means 3. But- means 4.

From there, most of the prefixes will be familiar from geometry class

and you can review them in tables and learn them.

I'm not gonna go through them all. There are a few naming rules that are specific to alkanes.

First, alkanes are always named based on the longest possible continuous chain in their structure.

For example, even though this looks like a 5 carbon chain intersecting with a 6 carbon chain,

it actually contains an 8 carbon chain if you look at it close enough.

So this is considered an octane with two carbon chain attached to one of its carbon atoms.

When shorter carbon chains are attached to longer ones like this, they're still named using the same prefixes,

but we stuff a little -yl onto the end to show that they're just attachments.

Since this attachment has two carbons, we call it an ethyl group.

And the attachment with just one carbon that turns amphetamine into methamphetamine, that's the methyl group.

Attachments are also given a number to show you where along the chain they're attached.

The long chain is always numbered carbon by carbon

in the direction that gives the attachments the lowest numbers possible.

So, if we number the chain the right way, the ethyl group will end up at position 4.

But if you do it the wrong way, it's in position 5.

Low numbers win so it's numbered from left to right in this case.

So when we put it all together, this compound is called 4 ethyl octane.

Congratulations! You just named an organic compound.

Now particularly astute and studious students would have noticed something here.

Earlier, I introduced you to isobutane, a compound with four carbons that are not all in a chain.

They call that isobutane and it is an isomer of butane,

but according to these all important rules of nomenclature, it's not actually any sort of butane at all.

The longest carbon chain is just 3 carbons long, so it's propane with one methyl group sticking off of it.

If we wanted to give a technical name for it, isobutane would be 2-methylpropane.

Though, since the second carbon is the only place where the methyl group can go without the molecule,

once again becoming butane, properly proper chemists just drop the two and call it methylpropane.

Now suppose you have more than one of the same size group attached to the same chain,

like two methyl groups on the same alkane.

In this case, you put a number for both of them

and then prefixes like di- and tri- are used to indicate multiple attachments.

So for instance, if an octane chain has methyl groups attached with second and fifth carbons,

it's called 2,5-dimethyloctane.

On the other hand, if you have attachments of different lengths,

you just name and number each one separately, being sure to list them in alphabetical order.

The structure we just used had a methyl group on it and an ethyl group on its fifth,

it would be 5-ethyl-2-methyloctane.

This is super useful for several reasons.

One, because there are trillions of ways that organic compounds can come together.

But also because you can work backwards from a name and build a structural formula from it.

Let's try that out. We're gonna build 2-ethyl-3,5-dimethylnonane.

Start with the main chain, nonane. The prefix non- indicates 9 carbons.

Then, add an ethyl group, a 2 carbon chain on number 4 and then methyl groups, just 1 carbon on carbons 3 & 5.

Our final step is to add enough hydrogen atoms to give every carbon atom 4 bonds.

And now, the molecule is complete. It's like a puzzle that we got to make.

Of course these compounds don't exist in isolation.

Like any other compound, they can undergo a whole variety of reactions.

But there are 3 types of alkane reactions that are important enough for us to cover right now right here.

The first is the kind that made alkane the most common fuel for combustion or burning.

You'll note here that I'm saying burning, a common misperception, even among chemistry students,

is that combustion somehow equals explosion.

While that would definitely make things more interesting, also more dangerous,

those two things are not synonymous.

Combustion is the type of reaction that powers your car and your propane grill,

even candles among many other alkane fuels.

The general reaction for combustion requires a hydrocarbon, oxygen, and a source of heat energy.

In this example, we're using methane, but it works the same for any pure hydrocarbon.

The only thing that changes is the coefficients.

The products of a complete combustion of a pure hydrocarbon are always

carbon dioxide and water vapor, just those two things.

The next major reaction that alkanes experience is halogenation,

when halogen atoms like fluorine or chlorine are substituted for one or more hydrogen atoms in the alkane.

For example, the rather well-known compound chloroform is more correctly called trichloromethane.

It's a molecule of methane that is reacted with a chlorine gas,

resulting in three of the hydrogen atoms being replaced with chlorine atoms.

The final reaction type is dehydrogenation, and it, somewhat obviously,

is the removal of hydrogen atoms from alkanes.

For example, ethane can be dehydrogenated by this reaction,

and as you can see, the result is that the carbon atoms are no longer saturated with hydrogen, thus,

requiring the formation of double or triple bonds to give the atoms the 4 bonds that they need.

Hydrocarbons that contain double or triple bonds have

their own specific groups with different rules, reactions, and properties than alkanes.

And those are the topic of next week's episode.

For now though, thank you for watching this episode of Crash Course Chemistry.

If you were listening, you learned about some of the different classifications of organic compounds,

the structure and properties of the simplest alkanes.

You also learned about isomers and why they're important, how to name an alkane based on its structure,

and how to build an alkane structure from its name.

And finally, you learned a few important types of chemical reactions that alkanes experience:

combustion, halogenation, and dehyrdogenation.

This episode was written by Edi Gonzalez, it was edited by Blake de Pastino,

and our chemistry consultant is Dr. Heiko Langner.

It was filmed, edited, and directed by Nicholas Jenkins. The script supervisor was Caitlin Hofmeister.

And Michael Aranda is our sound designer. Our graphics team, as always, is Thought Cafe.