IUPAC Nomenclature of Cyclic Compounds

Summary

This educational video script delves into cyclic compounds, contrasting them with linear ones. It explains the naming convention for cycloalkanes, using 'cyclo' as a prefix. The script clarifies that for cyclic compounds with substituents, the location isn't specified due to symmetry, but a numbering system is necessary for multiple substituents. It illustrates how to number rings to minimize locants and lists substituents alphabetically. The script also addresses prioritization in numbering for functional groups like double bonds and hydroxyl groups, providing clear examples for understanding.

Takeaways

• 🔄 **Cyclic Compounds**: Molecules can form cyclic structures called rings, like cycloalkanes.
• 📌 **Cycloalkane Nomenclature**: Cyclic hydrocarbons are named with the prefix 'cyclo' followed by the number of carbons.
• 🔄 **Cycloalkanes with Substituents**: For cyclic compounds with substituents, the position may not need to be specified due to symmetry.
• 🔢 **Numbering System**: A different numbering system is used for cyclic compounds, starting from any carbon and moving in either direction.
• 🏆 **Lowest Set of Locants**: The numbering system that gives the lowest set of locants for substituents is preferred.
• 🔄 **Direction of Numbering**: The direction (clockwise or counterclockwise) can affect the numbering of substituents on a ring.
• 📝 **Alphabetical Listing**: When there are multiple substituents, they are listed alphabetically after choosing the lowest locants.
• ➡️ **Functional Group Priority**: In cyclic compounds, functional groups like double bonds or hydroxyl groups take priority in numbering.
• 🔄 **Double Bond Positioning**: Double bonds in cyclic compounds are typically assigned the lowest possible carbon numbers.
• 💧 **Hydroxyl Group Priority**: Hydroxyl groups are prioritized in numbering, with the carbon bearing the hydroxyl often being carbon 1.
• 🔄 **Implicit Functional Groups**: The presence of certain functional groups can imply their position in the compound's name.

Q & A

What is the prefix used to indicate a cyclic compound in chemistry?

The prefix 'cyclo' is used to indicate a cyclic compound in chemistry.

How is a 3-carbon ring named in cyclic compounds?

A 3-carbon ring is named as cyclopropane.

What is the difference in naming substituents in cyclic compounds compared to linear compounds?

In cyclic compounds, due to symmetry, the location of a single substituent does not need to be specified, whereas in linear compounds, the position is indicated by a number.

Why is it not necessary to specify the location of a methyl group in methylcyclohexane?

It is not necessary to specify the location of a methyl group in methylcyclohexane because all six carbons on a cyclohexane are identical, and rotation can place the methyl group at any position without changing the molecule's identity.

How many possible ways are there to number a cyclohexane ring?

There are 12 possible ways to number a cyclohexane ring, as you can start on any of the six carbons and go either clockwise or counterclockwise.

What is the strategy for numbering substituents in a cyclic compound with multiple substituents?

The strategy is to choose the numbering system that gives the lowest set of locants possible for the substituents present.

How are substituents listed in the name of a cyclic compound with multiple substituents?

Substituents are listed alphabetically, with the prefix 'iso' being considered for alphabetical order.

What takes priority in the numbering scheme for cyclic compounds with functional groups?

Functional groups like double bonds or hydroxyl groups take priority over alkyl or halogen substituents in the numbering scheme for cyclic compounds.

How is the presence of a double bond accounted for in the numbering of a cyclic compound?

The two carbons participating in the double bond are numbered as 1 and 2 in some order, with the direction chosen to give other substituents the lowest possible numbers.

Why is the hydroxyl group prioritized in the numbering of a cyclic compound?

The hydroxyl group is prioritized because it is considered a functional group, and functional groups are given the lowest possible numbers in the IUPAC naming convention.

What is the name of a cyclohexane with a hydroxyl group and an ethyl group?

A cyclohexane with a hydroxyl group and an ethyl group is named 3-ethylcyclohexanol, with the hydroxyl group implied to be on carbon 1.

Outlines

00:00

🔍 Understanding Cyclic Compounds

This paragraph introduces cyclic compounds, specifically cycloalkanes, which are molecules that form ring structures. The prefix 'cyclo' is used to indicate a cyclic structure, followed by the number of carbons in the ring. For example, a 3-carbon ring is called cyclopropane. The paragraph explains that in cyclic compounds with substituents, the position of the substituent is not specified due to the symmetry of the ring, as rotation can make any position equivalent. However, when there are multiple substituents, a numbering system is necessary. The numbering system for cyclic compounds is chosen to give the lowest set of locants possible for the substituents. The paragraph also discusses how to number the ring and list substituents alphabetically, with examples of how to name a cyclohexane with multiple substituents. The concept of prioritization in numbering is also introduced, where certain substituents like double bonds or hydroxyl groups take precedence.

05:00

📚 Prioritization in Cyclic Compounds

This paragraph continues the discussion on cyclic compounds, focusing on the prioritization of substituents in the numbering scheme. It explains that in the presence of a double bond in a cycloalkene, the carbons involved in the double bond are assigned the lowest numbers, which in this case are 1 and 2. The direction of numbering is chosen to give other substituents the lowest possible locants. The paragraph provides an example of how to number a cyclohexene with a bromo substituent, emphasizing that the double bond's position is implied between carbons 1 and 2. It also discusses how a hydroxyl group takes priority in numbering over alkyl groups, with an example of a cyclopentanol with an ethyl substituent. The paragraph concludes with a call to action for viewers to subscribe for more tutorials and to reach out with questions.

Keywords

💡Cyclic Compounds

Cyclic compounds are molecules that form closed ring structures, as opposed to linear compounds which form open chains. In the video, cyclic compounds are introduced as an alternative to the linear compounds previously discussed. The video uses cycloalkanes as examples, which are hydrocarbons with a ring structure, like cyclopropane, cyclobutane, and cyclohexane. The concept is central to understanding the structural diversity of organic molecules.

💡Cycloalkanes

Cycloalkanes are a class of cyclic hydrocarbons with the general formula CnH2n. The video explains that these compounds are named using the prefix 'cyclo' followed by the number of carbons in the ring. Cycloalkanes are used to illustrate the basic concept of cyclic compounds and how they differ from their linear counterparts.

💡Substituents

Substituents are functional groups or atoms that are attached to a parent molecule. In the context of the video, substituents like methyl groups are added to cyclic compounds, changing their chemical properties and names. The video discusses how the position of substituents in cyclic compounds is determined and how it affects the naming of the compounds.

💡Symmetry

Symmetry in chemistry refers to the balanced arrangement of atoms in a molecule. The video highlights that cyclic compounds often have a high degree of symmetry, which simplifies the naming process since the position of a substituent like a methyl group on a cyclohexane does not need to be specified due to the ring's symmetry.

💡Numbering System

The numbering system in organic chemistry is used to specify the position of substituents on a molecule. The video explains that for cyclic compounds, the numbering system is different from linear compounds due to the lack of a clear left-to-right orientation. It is used to determine the lowest set of locants for substituents, which is crucial for the systematic naming of cyclic compounds.

💡Locants

Locants are numerical prefixes used in chemical nomenclature to indicate the position of substituents on a molecule. The video demonstrates how to choose the numbering system that gives the lowest set of locants for substituents in a cyclic compound, which is important for unambiguous naming.

💡Cyclohexane

Cyclohexane is a specific type of cycloalkane with six carbon atoms in a ring. It serves as a primary example in the video to explain the concepts of symmetry and substituents in cyclic compounds. The video uses methylcyclohexane to show how the location of a substituent is not specified due to the molecule's symmetry.

💡Cycloalkenes

Cycloalkenes are cyclic hydrocarbons that contain a carbon-carbon double bond. The video discusses how the presence of a double bond affects the numbering and naming of cyclic compounds, with the double bond's carbons typically being assigned the lowest possible numbers, such as 1 and 2.

💡Functional Groups

Functional groups are specific groups of atoms within molecules that determine the chemical properties of the compound. The video mentions that certain functional groups, like hydroxyl groups, take priority in the numbering scheme of cyclic compounds, indicating their importance in determining the structure and naming of the molecule.

💡Hydroxyl Groups

A hydroxyl group is a functional group consisting of an oxygen and hydrogen atom (-OH). The video explains that when a hydroxyl group is present in a cyclic compound, it takes priority in the numbering scheme, with the carbon bearing the hydroxyl group often being assigned the number 1.

💡Nomenclature

Nomenclature in chemistry refers to the systematic naming of chemical compounds. The video provides an in-depth look at how to name cyclic compounds with various substituents, emphasizing the importance of following IUPAC rules to ensure unambiguous communication in the scientific community.

Highlights

Introduction to cyclic compounds and the use of the prefix 'cyclo'.

Naming cyclic compounds with the same prefixes as linear compounds.

Cyclopropane, cyclobutane, cyclopentane, and cyclohexane are examples of cyclic compounds.

Cyclic compounds with substituents have unique naming conventions due to symmetry.

Methylcyclohexane is an example of a simple cyclic compound with a substituent.

In cyclic compounds, the location of substituents is not specified due to symmetry.

Multiple substituents in cyclic compounds require a numbering system.

There are 12 possible ways to number a six-carbon cyclic compound.

The numbering system prioritizes the lowest set of locants for substituents.

An example of numbering a cyclic compound with substituents 1, 2, and 4.

Alkyl and halogen substituents are listed alphabetically in cyclic compounds.

Cycloalkenes and cycloalkynes have different prioritization in numbering due to functional groups.

Double bonds in cyclic compounds are prioritized in numbering schemes.

The double bond is conventionally placed between carbons 1 and 2 in cyclic compounds.

Hydroxyl groups take priority over alkyl groups in cyclic compound numbering.

An example of numbering a cycloalkane with a hydroxyl group and an ethyl substituent.

The final names of cyclic compounds are derived from the lowest locants and alphabetical order of substituents.

Encouragement to subscribe for more tutorials and invitation to ask questions via email.

Transcripts

So, up until this point, we've been looking exclusively at linear compounds

but, molecules can also form cyclic structures that we call rings

here we can see some kinds of cycloalkanes, which end up just looking like these fun shapes.

basically, all the rules are the same, but for a cyclic compound, we are going to utilize the prefix "cyclo"

to indicate that it is cyclic, but the rest is the same.

a 3-carbon ring is a cyclopropane

4, cyclobutane, cyclopentane, cyclohexane, et cetera

we would use the same prefixes indicating the number of carbons that we already know.

now let's see what happens when we're looking at cyclic compounds with substituents.

let's take a look at a simple example, here we have a cyclohexane with a methyl substituent.

things are a little bit different with a cyclic compound

compared to a linear compound because of the symmetry

now, there's only one group here and it doesn't really matter where it is

because all six carbons on a cyclohexane are identical.

so this is simply methylcyclohexane, we do not have to indicate the location of the methyl group

because if it were on any other carbon, we could simply rotate it and it would be the same molecule.

so this is methylcyclohexane, that is sufficiently unambiguous.

however, when there are multiple substituents, we are going to have to use a numbering system

that is a little bit different from a linear molecule

because we no longer have a situation where it is left to right or right to left.

now there are actually 12 possible ways to number this ring, because we could start

on any of the six carbons, and then go either counterclockwise or clockwise.

however, we will choose the numbering system that gives the lowest set of locants possible

for the substituents that are present.

so let me show you what I mean, basically, let's say arbitrarily if we began here with carbon 1

and then went clockwise, this would be 1, 2, 3 and 4.

so we would have substituents on carbons 1, 3, and 4.

let's say we started here, and went counterclockwise. we would have a substituent on 3, 4, and then 6.

so you can see how there are many possible sets of locants, but the one that offers the lowest set of locants

is if we begin here and go counterclockwise

now the locants are 1, 2, and 4. so it doesn't matter what the substituents are

at least if they are alkyl or halogen

those are equal priority. so here, 1, 2, and 4 is the lowest set of locants possible.

then, by a separate algorithm, we are going to just list them alphabetically as we always do.

4-ethyl is going to be first

then actually isopropyl is before methyl because iso is the only prefix that is taken into account for alphabeticity

so that's 1-isopropyl

and then 2-methyl

cyclohexane

so once again, we chose 1, 2, 4 as the numbering system because that is the lowest possible

set of locants for those substituents, then we simply list them alphabetically as we normally would.

so we just looked at some cyclic compounds with alkyl substituents, but what if we were looking at

cycloalkenes or cycloalkynes, or cyclic compounds with hydroxyl groups.

these are the substituents that take priority over alkyl and halogen in terms of the numbering scheme.

let's look at how we're going to apply prioritization for cyclic compounds.

here we have a cycloalkene and the presence of the double bond means that we have to

give prioritization to that functional group in terms of the numbering scheme.

so when we have a double bond present in a cyclic compound, the two carbons that are participating

in the double bond are going to be carbons 1 and 2 in some order.

we have two options, either carbon 1 and 2, or 1 and 2.

we will choose one of those two directions so as to give any other substituents occurring sooner.

so we are going to have to number this 1, 2, 3, 4, because then the bromo group will occur on carbon 4

as opposed to 1, 2, 3, 4, 5, occurring on carbon 5.

so that is why we will number it this way

and so now, we are going to list the substituent, we have 4-bromo

but then we can simply say cyclohexene

and that is sufficiently unambiguous because it is a cyclic compound so we are

talking about a cyclohexene, and listing the location of the other substituent in relation to the double bond

so that is sufficiently unambiguous without saying where the double bond is

it is implied that the double bond is between carbons 1 and 2, because that's the convention we've used

to number the ring.

let's look at another compound with a hydroxyl group.

as you would expect, this hydroxyl group is going to take priority over the alkyl group in terms of numbering

so that means that the carbon that bears the hydroxyl will be carbon 1.

we're going to choose the direction to number so as to give the other substituent occurring sooner.

in this case, it's going to be clockwise because that will give the ethyl group on carbon 3 instead of 4 if we went the other way.

once again, we're going to say 3-ethyl and again it is implied that the hydroxyl occurs on carbon 1

so we can simply say cyclopentanol.

3-ethylcyclopentanol.

thanks for watching, guys. subscribe to my channel for more tutorials

and as always, feel free to email me with questions