Naming Alkenes, IUPAC Nomenclature Practice, Substituent, E Z System, Cycloalkenes Organic Chemistry
Summary
TLDRThis 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
🧪 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.
🔍 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.
🌀 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.
📚 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.
Mindmap
Keywords
💡Alkenes
💡Nomenclature
💡Cis and Trans Isomers
💡E/Z System
💡Substituents
💡Double Bond Position
💡Carbon Chain
💡Cycloalkenes
💡Suffixes
💡Numbering
💡Priority
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
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