The Basics of Organic Nomenclature: Crash Course Organic Chemistry #2

Summary

In this Crash Course Organic Chemistry episode, Deboki Chakravarti explores the complexities of chemical nomenclature and the importance of standardized naming conventions established by the International Union of Pure and Applied Chemistry (IUPAC). She explains the three-step IUPAC systematic naming process for organic compounds, which includes identifying the longest carbon chain, the highest priority functional group, and the types and positions of substituents. The video also highlights the difference between common names like 'vanillin' and systematic names, emphasizing the latter's utility in scientific communication. Examples are provided to demonstrate how to apply these rules, ensuring that viewers can effectively name and understand organic molecules.

Takeaways

• 🌐 The International Union of Pure and Applied Chemistry (IUPAC) was established in 1919 to standardize chemical nomenclature for clear communication among chemists worldwide.
• 🔍 IUPAC's systematic naming rules are crucial for accurately identifying organic compounds, which can be complex and have various possible structures.
• 📚 The three basic steps in IUPAC systematic naming are: identifying the longest carbon chain for the root name, adding a suffix for the functional group, and using prefixes for substituents and their positions.
• 🔢 For carbon chains with up to four atoms, mnemonics like 'Monkeys Eat Purple Bananas' (meth-, eth-, prop-, but-) can help remember the root names.
• 🔬 The presence and position of functional groups such as double (alkenes) and triple bonds (alkynes) are prioritized in naming to indicate where the 'action' in chemical reactions occurs.
• 🔑 Prefixes like 'di-', 'tri-', 'tetra-' indicate the number of identical substituents, and these prefixes are used in alphabetical order when multiple different substituents are present.
• 💧 Common names for chemicals, while easier to say, can be ambiguous and do not provide structural information, hence the importance of systematic IUPAC names.
• 🌐 The example of dichloromethane and methylene chloride illustrates how different names can refer to the same compound, highlighting the need for standardized naming.
• 📈 Understanding IUPAC nomenclature is essential for chemists to correctly interpret chemical structures and communicate effectively in the scientific community.
• 🔬 The video emphasizes the practical application of IUPAC rules, showing how they can be used to deduce the structure of a compound from its name and vice versa.

Q & A

What is the purpose of the International Union of Pure and Applied Chemistry (IUPAC) in the field of chemistry?

The IUPAC was established to unite the scientific community and ensure that chemists around the world could communicate accurately by providing standard rules for naming organic chemicals.

Why are common names for chemicals sometimes still used despite the existence of IUPAC nomenclature?

Common names are still used today probably because they are easier to say and remember, like 'vanillin' instead of '4-hydroxy-3-methoxybenzaldehyde', even though they might not be as useful for learning chemical structures.

What are the three basic steps in IUPAC systematic naming of organic compounds?

The three basic steps are: 1) Find the longest carbon chain and give it a root name. 2) Identify the highest priority functional group and add its suffix to the root name. 3) Identify the types of substituents and their positions on the carbon chain, then add a numbered prefix to the root name.

How do you determine the root name for a carbon chain with more than four atoms?

For carbon chains with five to twelve atoms, the root names are derived from geometric shapes, such as pent- for five atoms, hex- for six, and so on. For chains longer than twelve atoms, one would need to refer to a resource to find the appropriate root name.

What is the significance of numbering the carbons in a carbon chain when naming organic compounds?

Numbering the carbons is significant as it helps to communicate the position of functional groups and substituents along the chain, ensuring that the naming is consistent and understandable to all who follow the IUPAC rules.

How does the presence of a double bond affect the naming of an alkene?

The presence of a double bond in an alkene determines the root name and requires the numbering of the carbon chain to start from the end closest to the double bond, with the lowest possible number for the double bond, followed by the suffix -ene.

What is the difference between naming an alkane and an alkene according to IUPAC rules?

An alkane, which only has single bonds, is named by adding the suffix -ane to the root name derived from the longest carbon chain. An alkene, on the other hand, requires the inclusion of a double bond in the longest carbon chain and is named with the suffix -ene, with the double bond's position indicated by a number.

Can you provide an example of how to name a molecule with both a double bond and a triple bond using IUPAC rules?

An example would be a molecule with a seven-carbon chain, a double bond, and a triple bond. The root is hept-, and since alkenes have priority over alkynes in numbering, the double bond would be given the lower number. If a bromine is on carbon 4 and a methyl group on carbon 3, the name would be 4-bromo-3-methylhept-1-ene-6-yne.

What is the role of substituents in the IUPAC naming system, and how are they indicated in the name of a compound?

Substituents replace hydrogen atoms on a carbon chain and are indicated by prefixes that describe the substituent and its position on the chain. The prefixes are added in alphabetical order before the root name, and the position is indicated by a number.

How do you differentiate between 'dichloromethane' and 'methylene chloride' despite them being the same chemical?

While 'dichloromethane' follows the IUPAC naming rules indicating two chlorine atoms attached to a single carbon, 'methylene chloride' is a common name referring to a CH2- group with two chlorine atoms. Despite different names, the structural formulas result in the same compound.

Outlines

00:00

🔬 Introduction to IUPAC Nomenclature

This paragraph introduces the Crash Course Organic Chemistry series, highlighting the importance of standardized naming in chemistry. It explains the role of the International Union of Pure and Applied Chemistry (IUPAC) in establishing a global system for chemical nomenclature to ensure clear communication among chemists. The paragraph also touches on the historical use of common names for chemicals and how IUPAC's systematic naming helps in understanding chemical structures. The three basic steps of IUPAC systematic naming are outlined: identifying the longest carbon chain for the root name, adding a suffix for the functional group, and using prefixes for substituents and their positions.

05:02

🌐 Navigating Organic Chemistry Nomenclature

This paragraph delves into the specifics of naming organic compounds using IUPAC rules. It explains the process of identifying the longest carbon chain to determine the root name, with examples for chains containing up to twelve atoms. The paragraph also discusses how to handle functional groups in alkenes and alkynes, emphasizing the importance of numbering the carbon chain to indicate the position of double or triple bonds. The rules for naming substituents, such as methyl or halogen groups, are covered, including how to use prefixes and maintain alphabetical order. The paragraph provides examples to illustrate the application of these rules, ensuring a clear understanding of how to systematically name complex organic molecules.

10:02

🧪 Advanced IUPAC Nomenclature and Practical Examples

The final paragraph of the script builds upon the previous discussions by tackling more complex scenarios in IUPAC nomenclature. It addresses how to handle molecules with multiple functional groups and substituents, emphasizing the need to prioritize the numbering to give the functional groups the lowest possible numbers. The paragraph provides a detailed example of naming a molecule with both an alkene and alkyne functional group, illustrating the process of adding prefixes for substituents and ensuring alphabetical order. The paragraph concludes with a practical example comparing the common and IUPAC names for dichloromethane and methylene chloride, reinforcing the utility of standardized naming in chemistry.

Keywords

💡IUPAC

The International Union of Pure and Applied Chemistry (IUPAC) is a global organization that standardizes chemical nomenclature, ensuring that chemists worldwide can communicate accurately. In the video, IUPAC is highlighted as the authority behind the systematic naming of organic compounds, which is crucial for understanding and communicating about chemical structures and reactions.

💡Organic Chemistry

Organic chemistry is a branch of chemistry that focuses on carbon-containing compounds. The video emphasizes the complexity of organic chemistry nomenclature and how IUPAC's systematic naming rules simplify it. Organic chemistry is central to the video's theme as it discusses the naming of organic molecules, which is foundational for understanding their structures and properties.

💡Nomenclature

Nomenclature refers to the set of rules for naming things, especially in a scientific context. In the video, the term is used to describe the systematic way of naming organic compounds as established by IUPAC. Understanding nomenclature is key to the video's message, as it allows scientists to precisely identify and discuss chemical substances.

💡Functional Groups

Functional groups are specific groups of atoms within molecules that are responsible for the characteristic chemical reactions of those molecules. The video explains that functional groups, such as double and triple bonds in alkenes and alkynes, dictate the suffixes used in IUPAC naming, which is essential for understanding a molecule's reactivity and properties.

💡Substituents

Substituents are atoms or groups of atoms that replace hydrogen atoms in a hydrocarbon molecule. The video discusses how substituents are named and positioned in a molecule using prefixes and numbers, which is important for fully describing the structure of complex organic compounds.

💡Hydrocarbons

Hydrocarbons are organic compounds consisting only of hydrogen and carbon atoms. The video categorizes hydrocarbons into alkanes, alkenes, and alkynes, each with distinct bonding characteristics. Understanding hydrocarbons is fundamental to the video's theme, as they are the basis for more complex organic molecules.

💡Root Name

The root name in IUPAC nomenclature comes from the longest carbon chain in a molecule. The video explains that identifying the longest carbon chain is the first step in naming an organic compound, which sets the foundation for the rest of the naming process.

💡Suffix

A suffix in IUPAC nomenclature indicates the type of functional group present in the molecule. The video describes how suffixes like -ane for alkanes, -ene for alkenes, and -yne for alkynes are added to the root name to specify the molecule's structure and properties.

💡Prefix

A prefix in IUPAC nomenclature denotes the presence and position of substituents on a carbon chain. The video illustrates how prefixes like 'methyl-' and 'chloro-' are used to describe the type and location of substituents, which is crucial for detailing the exact structure of a molecule.

💡Dichloromethane

Dichloromethane is an example of a compound discussed in the video, where two chlorine atoms are attached to a single carbon atom. It serves as an example of how IUPAC nomenclature allows for clear and unambiguous identification of a chemical structure, even when common names like 'methylene chloride' might be used.

💡Lewis Structure

A Lewis structure is a diagram that represents the bonding of atoms in a molecule, including the valence electrons. The video briefly mentions Lewis structures in the context of completing the bonding around carbon atoms, which is a visual tool for understanding and verifying the correctness of IUPAC names.

Highlights

Introduction to Crash Course Organic Chemistry with Deboki Chakravarti.

Discussion on the importance of standardized chemical nomenclature for global scientific communication.

Historical context of IUPAC's establishment in 1919 to unify chemical naming conventions.

Explanation of how common names for chemicals can be misleading or confusing.

Introduction to IUPAC systematic naming with three basic steps.

Step 1: Finding the longest carbon chain to determine the root name.

Step 2: Identifying the highest priority functional group to add its suffix.

Step 3: Identifying substituents and their positions to add a numbered prefix.

Mnemonic 'Monkeys Eat Purple Bananas' to remember root names for short carbon chains.

Naming conventions for hydrocarbons: alkanes, alkenes, and alkynes.

How to number carbons in a chain to indicate the position of functional groups.

The significance of using the lowest numbers for consistency in naming.

Examples of naming alkenes and alkynes with their respective functional groups.

How to handle substituents in alkanes and the use of prefixes to indicate their presence.

The rule of thumb for substituent prefixes: lowest numbers and alphabetical order.

Practical example of naming a complex organic molecule with multiple functional groups and substituents.

Clarification of the dichloromethane and methylene chloride naming confusion.

Summary of the episode's key takeaways on organic compound naming.

Teaser for the next episode focusing on systematic names with heteroatoms.

Transcripts

You can review content from Crash Course Organic Chemistry with the Crash Course app available now for Android and iOS devices.

Hi! I’m Deboki Chakravarti and welcome to Crash Course Organic Chemistry!

Even when we speak the same language, we have different ways to say the same thing.

Do you call a carbonated beverage a “pop,” “soda,” or just “Coke”?

Or maybe you’re looking for a “drinking fountain” and everyone keeps pointing you to a “bubbler.”

Other times, we’re not saying what we think we mean.

For example, an American asking for chips in the UK isn’t going to get a bag of crispy potato circles.

If they shout out for their friend “Ken” in Japan, people might wonder why they’re yelling about a sword.

Or if they’re trying to say they’re embarrassed in Peru with a fragmented “I’m embarazada” -- they’re actually saying they’re pregnant.

Language is complicated, and it can be especially confusing in the chemistry lab.

If we ask our lab partner to pass the dichloromethane and they hand us a bottle labeled methylene chloride… is that the same chemical or not?

To unite the scientific community, the International Union of Pure and Applied Chemistry—otherwise known as IUPAC—was established in 1919.

This group wanted to make sure that chemists around the world could communicate accurately.

A hundred years later, IUPAC is still the guiding organization for all things nomenclature.

Thanks to them, we have some standard rules for naming organic chemicals!

[Theme Music]

By the time IUPAC came along with standard rules, organic chemistry as a field was already over 100 years old.

Many chemicals had common names given to them by the people who discovered them based on their source or smell or color.

For instance, vanillin is isolated from vanilla beans and cinnamaldehyde is isolated from cinnamon.

Alcohol, ether, acetone, and acetic acid are common names too.

While some common names might sound fun, you have to memorize them.

And they don’t tell you much besides, like, there’s a chemical responsible for the flavor in vanilla ice cream called vanillin.

Not super useful for learning chemical structures.

Sometimes chemists even disagreed about what each common name meant, sort of like regional differences about what to call a carbonated beverage.

Despite IUPAC’s best attempts to make organic chemistry nomenclature less confusing, many common names are still used today…

probably because “vanillin” is easier to say and put on a bottle than 4-hydroxy-3-methoxybenzaldehyde.

But that longer name is a systematic name that follows a set of rules, which means anyone who knows those rules can draw the structure.

There are three basic steps to IUPAC systematic naming.

We’ll add more as we discover more about organic molecules throughout this series.

But for now, these will get us started.

Number 1: Find the longest carbon chain and give it a root name.

Number 2: Identify the highest priority functional group and add its suffix to the root name.

And Number 3: Identify the types of substituents and their positions on the carbon chain, then add a numbered prefix to the root name.

So we start building any systematic name with the root name, which comes from the longest carbon chain in the molecule.

The word longest is key, because some molecules will have long chains sticking out that can throw you off!

So make sure to do a little extra counting to make sure you’ve actually found the longest one.

Carbon chains containing up to four atoms have arbitrary-sounding root names.

One carbon is meth-, two is eth-, three is prop-, and four but-.

This can be a little tricky to remember, but you can use this mnemonic to help: Monkeys Eat Purple Bananas.

For carbon chains with five to twelve atoms, the root names are similar to geometric shapes.

For example, a pentagon in geometry is a five-sided ring.

And if a carbon compound has the word pent- as its root, then it’s a five-carbon chain.

A six carbon chain is hex-, seven is hept-, eight is oct-, nine is non-, ten is dec-, eleven is undec-, and twelve is dodec-.

If you need a root name for a carbon chain with more than twelve atoms… I don’t have it memorized.

There are plenty of resources out there to look them up.

Chemists don’t usually deal with longer chains and there are plenty of other things to remember besides what a 56-carbon chain is called.

Back to our IUPAC rules.

Once we’ve counted our carbons and have a root name, we need to add a suffix to indicate what kind of organic molecule we’re dealing with.

The simplest organic molecules are hydrocarbons, which only have hydrogen and carbon atoms.

There are four kinds of hydrocarbons: alkanes, alkenes, alkynes, and aromatics.

But we’ll only talk about the first three for now, because smelly aromatic compounds are a little more complicated.

Alkanes only have single bonds between carbons.

For these compounds, we take the root name and tack on the suffix –ane.

For example, this skeletal structure is a six-carbon chain, so the root is hex-.

And because there are only single bonds, it’s an alkane, and we add the suffix -ane. It’s hexane!

Alkanes are kind of boring compared to their hydrocarbon cousins.

They’re low-energy couch potatoes and don’t interact with many other compounds.

On the other hand, alkenes and alkynes have functional groups.

Remember, last episode we said that functional groups are where all the cool chemistry happens!

In alkenes, the functional groups are double bonds between carbons, and in alkynes, the functional groups are triple bonds between carbons.

Alkenes and alkynes can do fun reactions to make things like light-emitting polymers,

which are big molecules with regions where electrons kind of move around on a kind of race track that absorbs energy and emits light…

But I’m getting ahead of myself!

To name an alkene, we find the longest chain of carbon atoms and it must include a double bond.

If the longest carbon chain doesn’t include a double bond, it’s not named as an alkene.

Sorry, I don’t make the rules, IUPAC does.

Since IUPAC rules are all about communication, we want to let people know where that double bond is on the chain.

So we’ll number the carbons, starting on the end closest to the double bond.

For the sake of consistency, we want to keep the numbers as low as possible.

Then, we’ll take the lowest number touching the double bond, combine it with the suffix -ene, and add that to the root name of our chain.

For example, the longest chain in this molecule is a five-carbon chain, so the root is pent-.

Because there’s a double bond, we know the suffix is -ene but we also have to number the carbons.

Starting from the end closest to the double bond, that’s 1-2-3-4-5.

And because the double bond is between carbons 1 and 2, this compound is pent-1-ene.

Notice the punctuation here: we stick dashes around the number.

To name alkynes, the hydrocarbons with a triple bond, we do the same thing.

First, we find the longest chain of carbon atoms and pick a root name.

Then, we number the chain from the end closest to the triple bond to let people know where it is, and tack on the suffix -yne.

For example, an eight-carbon chain with a triple bond in the center would be called oct-4-yne.

To finish the IUPAC rules, once we have a root name and suffix, we might be done if the molecule doesn’t have anything fancy going on!

But frequently, organic molecules have substituents, where plain old hydrogens on a carbon chain can be replaced by other carbon chains or halogen atoms like chlorine, bromine, and iodine, for example.

We communicate where substituents are by adding prefixes before the root name.

Plus, just like we had to count carbons for alkenes and alkynes, we need to communicate where every substituent has done its substituting.

If we’re dealing with an alkane, where the longest carbon chain only has single bonds, we’ll number the chain so that the carbon atoms with the substituents get the lowest numbers.

For example, let’s take our hexane from before and replace one hydrogen on a carbon with a -CH3 group.

So in this case, we have an alkane, and we want to number the longest 6-carbon chain so that the carbon with the substituent is 2 not 5.

Remember, we want to keep the numbers as low as possible!

The -CH3 group takes the same name as a 1-carbon-chain root, meth-.

And because this group is a substituent it gets a new ending spelled -y-l.

So the prefix we add is 2-methyl, to communicate where and what it is.

And this compound is 2-methylhexane.

If the molecule is flipped over, we could start from the left and it would still be 2-methylhexane!

They’re the same compound, no matter if the methyl is drawn on the right or the left.

If we have two or more of the same substituents, we add di-, tri-, tetra- and so on to the prefix.

So if we took 2-methylhexane and added another -CH3 group to a different carbon, we get 2,4-dimethylhexane.

Notice the punctuation here, too: the numbers are separated from each other by a comma, and are separated from the words by a dash.

But there are other substituents besides carbon chains.

Let’s say we take our 2,4-dimethylhexane and replace a hydrogen atom on carbon-3 with a halogen like a chlorine atom.

So the molecule name gets another prefix!

Halogens get the -ine in their name replaced with the letter -o.

So chlorine becomes chloro-, bromine becomes bromo-, and iodine becomes iodo-.

That means we need to tack on the prefix 3-chloro here.

Lastly, when we add substituent prefixes, IUPAC rules say we need to put them in alphabetical order.

And the multipliers di, tri, and tetra do not count when we’re alphabetizing.

So this molecule is named 3-chloro-2,4-dimethylhexane.

These rules about substituent prefixes are mostly the same for alkenes and alkynes.

Except, when it comes to numbering the chains, the double and triple bonds between carbon atoms have priority over substituents sticking out.

So we start numbering the chain closest to the bonds instead of the substituents.

If we take our alkene friend pent-1-ene and add a ethyl group (that’s two carbons and six hydrogens) at carbon 3, we’d name this 3-ethylpent-1-ene.

Or if we put two methyl groups on the 2nd and 7th carbons of the alkyne oct-4-yne, meet the spectacular 2,7-dimethyloct-4-yne.

Now that we have the basics, we can start naming any compound!

Even if they look kinda complicated with more than one functional group and substituent.

Like this molecule:

But we got this! Don’t worry!

We have our trusty steps.

Number 1: Find the longest carbon chain and give it a root name.

In this case, we see there’s a seven-carbon chain here, so the root is hept-.

Number 2: Identify the highest priority functional group and add its suffix to the root name.

Alkenes and alkynes have equal priority when it comes to numbering.

But when an alkene and alkyne tie for lowest number, the alkene wins.

We’ll count from both ends to see what’s up.

And look: because the alkene and alkyne tie for lowest number, the alkene wins.

So we’ll use the numbering where the double bond is lower.

Now we have to name our double- and triple-bond functional groups, and the alphabetical order rule still applies here.

So with the root and the suffix combined, we have hept-1-ene-6-yne.

Finally, number 3: Identify the types of substituents and add a numbered prefix to the root name.

In this case, there’s a bromine on carbon 4 and a methyl group on carbon 3.

Taking alphabetical order into account, we add 4-bromo-3-methyl before the root and suffix.

And we’ve conquered this puzzle!

It’s 4-bromo-3-methylhept-1-ene-6-yne.

It’s kind of a mouthful to say, but so much more useful to chemists than if I named it Debokiyne or something.

Now, remember that conundrum from the beginning, when we asked our lab partner for dichloromethane and got a bottle of methylene chloride?

Let’s build those molecules.

Looking at the name dichloromethane, we know from meth- that this is a single carbon and -ane that it’s an alkane with single bonds.

The dichloro- tells us that we have two chlorine atoms connected to the only carbon, no substituent number required.

That’s the skeletal structure.

And if we want to get all fancy with a Lewis structure, we know that carbon often makes four bonds, so we can add two hydrogen atoms to finish it off.

Methylene chloride is trickier because we can’t use our IUPAC rules.

We just need to know that methylene is a common name for a CH2- group.

Then, because chloride is in the name, we can get to the final structure by filling in the two open spots with chlorine.

The end structure is the same, so our lab partner did know what they were doing!

But calling this compound dichloromethane makes it easier for scientists to know they’re talking about the same thing.

In this episode, we learned that:

There are three steps to naming molecules, which include the root name, a suffix based on functional groups, and a prefix based on substituents.

And we number the longest carbon chain by giving the highest priority functional group the lowest possible number, or whatever gives the substituents the lowest possible numbers.

Next time, we’ll learn how to give molecules systematic names when they have functional groups with heteroatoms!

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