Naming Alkenes, IUPAC Nomenclature Practice, Substituent, E Z System, Cycloalkenes Organic Chemistry

Summary

This video script offers a comprehensive guide to alkene nomenclature, covering basic naming conventions, the distinction between cis and trans isomers, and the use of the Enz system for more complex molecules. It explains how to identify the longest carbon chain, assign numbers to double bonds for the lowest possible values, and determine the priority of substituents using atomic numbers. Examples are provided to illustrate the process of naming alkenes, including those with multiple double bonds and various substituents.

Takeaways

• 🔡 Alkene nomenclature begins with the common names of alkanes, followed by a suffix indicating the number of carbons and the presence of a double bond.
• 📏 The numbering of alkenes starts from the end nearest to the double bond to give it the lowest possible number.
• 🔄 The terms 'cis' and 'trans' describe the orientation of substituents around a double bond, with 'cis' being on the same side and 'trans' on opposite sides.
• 🔎 The IUPAC 'E'/'Z' system is used for more complex alkenes with multiple substituents, where 'E' indicates the highest priority groups are on opposite sides and 'Z' indicates they are on the same side.
• 🌐 The longest carbon chain containing the double bond is chosen for naming, and the double bond position is given the lowest possible number.
• 🏋️‍♂️ Priority of substituents is determined by atomic number, with larger atoms and groups having higher priority.
• 📚 Common alkane names are methane, ethane, propane, butane, pentane, hexane, heptane, octane, nonane, and decane.
• 🔗 When two double bonds are present, the suffix 'diene' is used, and a comma separates the positions of the double bonds.
• 🔄 Cycloalkenes are named by adding '-ene' to the cycloalkane name, with the double bond assumed to be at carbon 1 unless otherwise stated.
• 📐 For alkenes with functional groups like halogens, the position and type of the functional group are indicated in the name.
• 🧪 The 'E'/'Z' notation is placed before the name of the alkene to specify the stereochemistry of each double bond.

Q & A

What is the common name for a four-carbon alkane?

The common name for a four-carbon alkane is butane.

How do you name an alkene with a double bond between carbons one and two?

An alkene with a double bond between carbons one and two is named as '1-butene'.

When naming alkenes, what is the preferred direction to count from to get the lowest numbers?

When naming alkenes, you should count from the direction that gives the lower numbers for the double bond.

What is the name of an alkene with a five-carbon chain and a double bond on carbon 2?

An alkene with a five-carbon chain and a double bond on carbon 2 is named '2-penene'.

How do you name an alkene with two double bonds?

An alkene with two double bonds is named with the suffix 'diene' and the positions of the double bonds are separated by a comma.

What is the name of a cycloalkene with a double bond?

A cycloalkene with a double bond is named by adding the suffix 'ene' to the name of the cycloalkane.

How do you name a cycloalkene with a double bond in a ring?

A cycloalkene with a double bond in a ring is named by adding the suffix 'ene' to the name of the cycloalkane, and the double bond is assumed to be on carbon 1 unless otherwise specified.

What is the difference between 'cis' and 'trans' isomers in alkenes?

In alkenes, 'cis' isomers have similar groups on the same side of the double bond, while 'trans' isomers have similar groups on opposite sides.

How do you determine the priority of substituents for the E/Z nomenclature?

The priority of substituents for the E/Z nomenclature is determined by atomic number, with higher atomic numbers having higher priority.

What is the name of an alkene with a double bond at carbon 1 and a methyl group on carbon 3?

An alkene with a double bond at carbon 1 and a methyl group on carbon 3 is named '3-methyl-1-cyclohexene'.

How do you name an alkene with multiple substituents attached to the double bond?

For alkenes with multiple substituents attached to the double bond, you use the E/Z system to determine the stereochemistry and then name the longest chain with the substituents in alphabetical order.

Outlines

00:00

🧪 Basics of Alkene Nomenclature

This paragraph introduces the basic principles of alkene nomenclature. It explains how to name alkenes based on the number of carbon atoms, using alkanes as a reference. For example, a four-carbon alkane is butane, and an alkene with a double bond between carbons one and two is named '1-butene'. The paragraph also discusses how to determine the position of the double bond by choosing the direction that gives the lower numbers, and the importance of adding the suffix 'ene' to indicate the presence of a double bond.

05:00

🔍 Advanced Alkene Naming

This section delves into more complex alkene naming scenarios, such as alkenes with multiple double bonds. It explains how to use a comma to separate numbers when there are two double bonds and a hyphen to separate a number from a substituent group. The paragraph also addresses the naming of cycloalkenes, where the double bond is assumed to be on carbon one unless specified otherwise, and the process of determining the direction for numbering to achieve the lowest possible numbers for the double bonds.

10:02

🌀 Cycloalkenes and Stereochemistry

This paragraph focuses on the naming of cycloalkenes, including those with substituents like bromine. It discusses the priority of the double bond over other substituents in the naming process and introduces the concept of stereochemistry with cis and trans isomers. The paragraph explains how to determine the configuration of double bonds using the terms 'Z' (similar to cis) and 'E' (similar to trans), based on the relative positions of the highest priority groups attached to the double bond.

15:03

📚 The IUPAC System for Complex Alkenes

The final paragraph provides an in-depth look at naming more complex alkenes using the IUPAC system. It covers how to identify the longest chain that includes the double bond and how to assign the lowest numbers to the double bonds. The paragraph also explains the use of the Z/E notation for double bonds with different substituents and how to list substituents in alphabetical order when naming alkenes. It concludes with an example of naming a complex alkene with multiple double bonds and substituents.

Keywords

💡Alkenes

Alkenes are a class of hydrocarbons with at least one carbon-carbon double bond. They are a fundamental topic in organic chemistry. In the video, alkenes are the central focus, with discussions on how to name them correctly using IUPAC nomenclature rules.

💡Nomenclature

Nomenclature refers to the systematic naming of chemical compounds. In the context of the video, it specifically refers to the rules and conventions for naming alkenes, including the use of prefixes, suffixes, and numbers to indicate the position of the double bond and substituents.

💡Cis and Trans Isomers

Cis and trans isomers are geometric isomers of alkenes where the position of the substituents around the double bond differs. Cis isomers have similar groups on the same side of the double bond, while trans isomers have them on opposite sides. The video explains how to distinguish between these isomers and includes examples like 'trans-2-pentene' and 'cis-2-pentene'.

💡E/Z System

The E/Z system is a method for naming geometric isomers of alkenes, where 'E' stands for 'entgegen' (German for opposite) and 'Z' stands for 'zusammen' (German for together). The video discusses how to use this system to determine the configuration of double bonds when there are different substituents attached to the carbons of the double bond.

💡Substituents

Substituents are the functional groups or atoms that replace hydrogen atoms in a hydrocarbon. The video explains how substituents affect the naming of alkenes and how they are prioritized in the E/Z notation system.

💡Double Bond Position

The position of the double bond in an alkene is crucial for its naming. The video emphasizes the importance of numbering the carbon chain in a way that gives the double bond the lowest possible number, which is a fundamental principle in IUPAC nomenclature.

💡Carbon Chain

The carbon chain refers to the sequence of carbon atoms in a molecule. In the video, the process of identifying the longest carbon chain to serve as the base for naming an alkene is explained, which is essential for determining the root name of the compound.

💡Cycloalkenes

Cycloalkenes are alkenes that contain a ring of carbon atoms. The video mentions how to name these compounds, such as 'cyclohexene', and how the presence of a double bond in the ring affects the naming.

💡Suffixes

In alkene nomenclature, suffixes like '-ene' indicate the presence of a double bond. The video explains how to add these suffixes correctly to the names of alkenes, such as changing 'butane' to 'butene' when there's a double bond.

💡Numbering

Numbering in alkene nomenclature refers to the practice of assigning numbers to carbon atoms to indicate the position of the double bond and substituents. The video demonstrates how to number carbon chains to achieve the most simplified and correct naming of alkenes.

💡Priority

Priority in the context of the E/Z system refers to the ranking of substituents based on their atomic number. The video explains how to determine the priority of substituents to correctly assign the E or Z configuration to a double bond.

Highlights

Basic nomenclature of alkenes is discussed, including the naming of alkanes and alkenes.

The importance of choosing the lower number for the position of the double bond in alkene naming is emphasized.

Explanation of how to name alkenes with the double bond at different carbon positions.

Introduction to the concept of E and Z isomers in alkenes.

The Enz naming system for complex alkenes with multiple substituents is introduced.

Guidelines for naming alkenes with multiple double bonds, using the suffix 'diene', 'triene', etc.

How to name cycloalkenes, including the assumption of double bond position in rings.

The difference between trans and cis isomers in alkenes and how they are named.

The process of identifying the longest carbon chain when naming alkenes.

How to name alkenes with substituents like bromine and methyl groups using the Enz system.

Explanation of how to determine the priority of substituents in the Enz system.

An example of naming an alkene with multiple double bonds using the Enz system.

How to handle alkenes with different substituents on the same carbon when naming them.

The naming of alkenes with complex substituents using the Enz system, including the alphabetical order of substituents.

A comprehensive example of naming an alkene with multiple double bonds and various substituents.

The significance of the position of the double bond in the naming of alkenes, even with complex substituents.

Conclusion of the video with a summary of the key points in alkene nomenclature.

Transcripts

in this video we're going to go over the

nomenclature of alkenes we're going to

talk about the cysts and trans uh isomer

and also the Enz naming system but let's

start with the

basics so how can we name this

particular

alen now the first thing you need to

know is the common names of the alkanes

from 1 to 10 a one carbon alcane is

known as methane a two carbon alane

ethane three is for propane four forane

five pentane six hexane seven heptane

eight octane nine ning 10

decking so in this particular uh

compound we

have four carbon atoms so that's

associated with butane but because we

have an alkine it's going to be

buttine and the double bond is between

carbons one and two but you need to pick

the lower number of those two so this is

known as one

buttine some textbooks might write it

this way but one in so you can also

write it that way as

well now what about this

example how would you name this

particular

alen so should we count it from the left

side or from the right side if we count

it starting from the left notice that

the Aline is on carbon 3 but if we count

it from the right side notice that it's

on Carbon 2 and you want to count it in

such a way that um you will get the

lower numbers so this is going to be

called two penene since we have a five

carbon chain don't forget to add the

suffix for alkenes whenever you have a

double bond

try this

example now if we count it from the left

the alen will be on carbon 3 if we count

it from the right it would still be on

carbon 3 however the methyl will be on

carbon 5 if we count it from the left

the methy would be on Carbon 2 so

therefore you want to count it from left

to

right so this is going to be two methyl

dash3 D

hexene since the double bond is on

carbon 3 and a six carbon chain is

hexane but we got to add the suffix

in now how about this example what if we

have two double bonds what should we do

in this case now we have a total of four

carbons which is associated with the

name

butane but since we have two double

bonds we need to add the suffix dine for

the two double

bonds so we have a double bond at one

and at three so it's called 1 comma 3

buta

dying the use of a comma is required to

separate two numbers and the use of a

hyphen is required to separate a number

and a

go ahead and try this

example so what direction should we

number it from the left or from the

right if we start from the left the

double bond will be at one if we start

on the right it's going to be at

two and the other one is going to have a

much higher number let's count them both

ways so this will be 1 2 3 4 5 6 and 7

that means we will have a double bond at

1 and five if we count it the other

way we're going to have a double

bond at 2 and six so one is lower than

two so let's count the other

way so we have a methyl on carbon 3

let's begin with that so this is going

to be three methyl

Dash now we have a double bond at one

and five so it's one comma five and it's

a seven carbon chain so we're dealing

with heptane but instead of saying

heptane it's going to be hepti

dine and so that is the name of this

particular

molecule now what about cyc alenes so

what if we have a double bond in a ring

how can we name it

instead of saying

cyclohexane this is simply

cyclohexene and if you only have a

double bond one one in a ring it's

automatically assumed to be carbon one

so you don't have to say one cyclohexene

you could just simply say cyclohexene

because the double bond has to be on

carbon

one so knowing

that what is the name of this particular

molecule feel free to pause the video as

you work out this

example now if we choose to count it

this way the methyl will be on carbon 5

however if we choose to count it this

way the methyl will be on carbon 3 so

let's count it that way this is going to

be three

methyl cycop penene since it's a five

carbon

ring and we don't have to say three

methyl-1 cyop penine as we've mentioned

mention before the double bond is on

carbon

one now what about this

example let's name this

molecule now the double bond has more

priority than the bromine atom

in terms of naming so we're going to

start counting from the double bond we

want to count it this way we want the

double bonds to have the lowest

numbers if we start from the

middle it's just not going to work out

that

way we'll have a double bond at 1

3 and six as opposed to 1 3 and

five so this is the way we should count

it so it's going to be called seven

bromo Dash we have a double bond at 1 3

and five so 1 comma 3 comma

5 and it's a seven carbon ring so we're

dealing with heptane or cycloheptane so

it's

cycl Heep

Trine since we have three double bonds

dine is for two double bonds Trine is

for three tetraene in case you have

four try this

one now in this particular example you

need to identify the longest chain and

you want the double bond to be included

in the longest chain

and you want to get the double bond the

lowest number so you want to start

counting here this is going to be 1 two

3 4 and it's not this is not the longest

chain the longest chain actually

contains seven

carbons so we have a heptane or

heptin now this is an ethyl group

because it has two carbons and this is

another ethyl group so we have an eth

group on carbons two and four so this is

going to be called

24 DL

dash1 heptin since double bond is on

carbon

one what is the name of these two

alkenes we talked about this one earlier

in the

video if we number it we could see that

we have a five carbon chain and a double

bond at two so this is called two

penene however if you if you look at the

one on the right it's also um called two

penene so what is the difference between

these two molecules because they're not

exactly the

same double bonds are not free to rotate

and so these are actually two different

molecules

on the left notice that the hydrogens

that are connected to the double bond

they're opposite to each other but on

the right they're on the same

side this is the trans isomer and on the

right we have the CIS isomer so this is

called

trans T penene and this is CIS T

penene now for more complicated examples

where you have

a lot of different substituents attached

to the double bond you may want to use

thez

system so first let's

determine if we have the e isomer or the

Z

isomer the E isomer is similar to the

trans isomer and the Z isomer is similar

to the CIS

iser now what you need to do is

determine which group has a higher

priority and it's based on the atomic

number so if we compare bromine and

carbon you need to pair two groups on

the same carbon

atom or attached to the same side of the

double

bond bromine has a higher atomic number

than carbon so bromine has a higher

priority than carbon now between methyl

and hydrogen methyl wins because carbon

has a higher atomic number than

hydrogen now if the two highest

priorities are on the same side you have

the Z

isomer if they were on opposite sides

that would be the E isomer will be

trans-like so to

speak now what about naming this

particular molecule what is the name for

it so let's identify the longest chain 1

2 3 4 we want to count from left to

right so that the Broan atom is on

Carbon 2 instead of carbon

3 so this is going to be

called Z since we have the Z isomer

Dash two

bromo das2 buttine

now what about this

example how can we name this particular

alen so first let's determine if we have

the e isomer or the Z isomer and let's

make it a little bit more interesting

let's make this a

ch3 now you can't say it's CIS or trans

because you don't know which two groups

to compare to if you had two hydrogens

let's say this was a hydrogen

then you could say it's Cy because the

two hydrogens are on the same side but

when you have four different groups you

can't really describe it in terms of Cy

or trans you need to use the Enz system

so let's compare chlorine and hydrogen

which of these two groups have the

highest priority well chlorine has a

higher atomic number so it's going to be

chlorine now if we compare the ethyl

group and the methyl Group which one has

more

priority well ethyl is going to win

against methyl since it has more

carbons so notice that the two highest

groups are on the same side so we have

another Z isomer so this is going to be

called

Z and then let's identify the longest

chain so it's going to be carbon 1 2 3

4 so we have a chloro on one a methyl on

two and let's put it in alphabetical

order so it's one

chloral Das 2

methyl

dash one buttine since we have four

carbons total in the longest

chain now let's try a harder

example let's try this one

so take a minute and see if you can name

this particular alen including with the

andz

system now the first thing I would do is

identify each alen is being each double

bond as being e or

Z so let's draw the hydrogens that are

located on each of these double bonds so

if we compare the hydrogen and the

methyl the methyl group has uh more

priority and if we comp compare chlorine

and this

group so you're looking at the carbon

atom first versus the chlorine chlorine

has a higher atomic number than carbon

so chlorine has more

priority so the highest groups are on

the same side therefore this is the Z

isomer now let's focus on the next

double

bond on this side of the double bond

we're comparing the methyl and the ethyl

group The ethyl group wins because it

has more carbons and on this side of the

the double bond we're comparing the

hydrogen compared to this and hydrogen

always

loses with the exception of comparing it

to another hydrogen atom which will be

pointless so this side has the higher

priority so notice that this is the E

isomer for it to be the Z these two

would have to have the highest priority

or these two because those would be on

the same side but these two groups are

on opposite sides so we have the e

isomer

now let's put it

together so let's identify the longest

chain we want to count from left to

right so that the first alen will have a

number of two instead of

three so this is going to be 1 2 3 4

five 6 7

8 now the double bond at two is

associated with the Z isomer so we're

going to put 2 Z and that five is

associated with the E isomer so if you

have two or more double bonds you need

to put the number next to the e or z

letter to

specify each double bond and its

specific uh stereo chemistry so to

speak now we have a chloro group on

three and a methyl on six so let's put

it in alphabetical order it's going to

be three

chloro Dash six

methyl

Dash we have a double bond on two and

five so 2 comma 5

Das OCTA since we have a total of eight

carbons OCTA D since we have two double

bonds and that is it for this video

thanks for watching and have a great day