IUPAC Nomenclature Rules Explained In 10 Minutes

First, let's start with nomenclature of

alkanes. Rule one, how to identify the

longest parent chain. The first step is

to find the longest continuous chain of

carbon atoms. Keep in mind that it is

not necessary that the chain should be

straight or linear. Let's understand it

with some examples. Look at this

structure. If we consider the straight

chain, it has five carbons. But if we

consider the carbons that are not

involved in the linear structure, then

it has six carbons. So, the correct way

is to select this longest possible chain

which has the maximum possible number of

carbons in it. Rule two, how to number

the parent chain. If the parent chain

has no branch, the numbering can start

from any side. To understand it, take

this structure. It has five carbons and

all carbons are present in the parent

chain. It means it has no branch. So,

its name will be npentane and we can

start numbering from any side. Keep in

mind that here N refers to the structure

having no branch. But if the parent

chain has a branch, then numbering will

start from the side that gives the least

number to the branch attached. Let's

take the following structure as an

example. If we start numbering from

right to left, the substituent or branch

is present at the fourth carbon. But if

we consider it from left to right, the

branch is attached at the second carbon.

So according to the rule, numbering

should start from left to right as it

gives the least number to the branch

attached. Rule three, how to name the

substituents. The substituents are named

based on the number of carbons they

have. For example, if the branch has one

carbon, it is called methyl. And if it

has two carbons, it will be called

ethel. Actually, it's very easy to name

a branch. just change the name ending in

a ne to Y L. For example, as we know one

carbon is called methane and if one

carbon is present as a branch then its

name will become methyl. Similarly, if

two carbons are present as a branch or

substituent, then the name ethane will

change to ethl. Let's take these two

structures as an example. Since the

first structure has one carbon as a

branch, it will be called methyl and the

second structure has two carbons. So,

the name of the branch will be ethyl.

Rule four. How to write the complete

name of a structure. First write the

number of the carbon on which the

substituent or branch is attached. After

that write the name of the branch

attached and at the end write the total

number of carbons present in the parent

chain. To understand this let's take the

following structure as an example. It

has a methyl group as a substituent.

Since from both sides the number of the

substituent will be the same which is

two. We can assign the number from

either side. The total number of carbons

in the parent chain is three. So

according to the rule the name of this

structure will be two methyl propane.

Let's take another example to understand

it more deeply. In this structure, the

branch attached contains two carbons, so

it will be called ethel. And the total

number of carbons in the parent chain is

seven. Numbering will start from the

right side because it gives the least

number to the branch attached. By

following all the above mentioned rules,

the name of the structure will be two

ethyl heptine. Rule five, how to name

multiple substituents. First, let's

focus on what to do if the same

substituent is present on more than one

carbon. In this case, we name the

substituents by using prefixes such as

di tetra and so on. One thing you need

to keep in mind is that we have to write

the number of each carbon that contains

a branch or substituent. Let's take this

structure as an example. It has two

methyl groups as branches and they are

present at positions 2 and four. So in

order to name this structure, first we

have to write the number of each carbon

that contains a branch. The overall name

will be two four dimethylhexane. But

what if the branches are different from

each other? For example, if one branch

is methyl and the other is ethl. In this

case, we need to follow alphabetical

order. Since E comes before M, we have

to write Ethel first and after that we

can write methyl. Let's take the

following example to make it clear. The

name of the structure will be two ethyl

3methylhexane. Rule six. How to name

cyclic alkanes? It is very easy to

assign names to cyclic alkanes. If the

structure has a ring, we need to add the

prefix cylo before the parent chain

name. For example, this structure has

four carbons and they are in ring form.

So its name will be cyclloutane. Now

let's move towards the nomenclature of

alkenes. Rule one, select the longest

possible chain that contains the double

bond. Keep in mind if you select a chain

that has the maximum number of carbons

but does not contain the double bond, it

will be incorrect. The reason is that

here we need to prefer the double bond

over the single bond and the chain must

include the double bond. To understand

this deeply, let's take the following

example. This structure has six carbons

in a straight chain but the double bond

is not present in it. However, if we

select the chain that contains the

double bond, it has four carbons. So,

according to the rule, the parent chain

with four carbons is correct because it

also contains the double bond. Rule two,

how to number the parent chain and

branches. If the parent chain contains a

double bond, the numbering should be

done in such a way that it gives the

least number to the double bond. Keep in

mind here we should not prioritize the

branch for numbering. Since the parent

chain contains a double bond, we should

prefer to give the least number to the

double bond rather than the branch

attached. Let's take the following

example to understand this. Since the

double bond is present on the second

carbon, numbering will start from left

to right as it gives the least number to

the double bond. Rule three, how to name

the parent chain having a double bond.

If the parent chain does not contain any

branches or substituents, the name

should be given in such a way that the

position of the carbon containing the

double bond is mentioned first. After

that, the total number of carbons in the

parent chain is indicated ending the

name with E and E. Let's make this clear

with this structure. Since the parent

chain has five carbons and the double

bond is present at the second carbon,

its name will be two pentine. Rule four,

how to name a branched chain structure

having a double bond. One thing to keep

in mind is that while writing the name

of compounds, whether they contain a

double or single bond, we need to

mention and write the substituent or

branch at the start of the name. For

example, let's take this structure to

understand this. Since a methyl group is

present on the third carbon and the

double bond is present on the second

carbon, the name of this compound will

be threemethyl 2 butine. Rule five, how

to name multiple branches in a double

bond. If the parent chain has more than

one similar branch, we need to use

prefixes such as dri and tetra. However,

if it contains different branches, we

need to follow alphabetical order just

like in the case of alkanes. Look at

this structure. It has a double bond at

the first carbon, two methyl groups

attached at the third carbon, and an

ethyl group on the fourth carbon. Since

the substituents are different, we need

to follow the alphabetical rule. Its

name will be four ethyl 333

dimethylhexene. Rule six, how to name

more than one double bond in a

structure. If there is more than one

double bond, use prefixes like dyen for

two double bonds, try ena for three, and

so on. Don't forget to number the

positions of all the double bonds. Have

a look at this structure. It has two

double bonds at carbons 1 and three. So

its name should be one. Three but dyene.

Rule seven. How to name cis and trans

isomers having double bonds. To

understand this, let's take the example

of two butin. If both methyl groups are

present on the same side of the double

bond, it will be called cis 2butine. But

if both methyl groups are present on

opposite sides of the double bond, it

will be called transbboutine. And now

finally let's move towards the

nomenclature of alkyes. Rule one. Select

the longest possible chain that contains

the triple bond. When naming alkyes, the

first step is to identify the longest

continuous carbon chain that includes

the triple bond. Even if another chain

has more carbons but does not include

the triple bond, it would not be

considered the correct parent chain.

This is because the triple bond is given

priority over single bonds when

selecting the main chain. Let's take an

example to understand this better.

Imagine we have a structure with six

carbons in a straight chain, but the

triple bond is not part of it. If we

select the chain containing the triple

bond, it has five carbons. According to

this rule, the five carbons chain is the

correct parent chain because it includes

the triple bond. Rule two, how to number

the parent chain and branches. Once the

parent chain is selected, the next step

is to assign numbers to the carbons in

the chain. The numbering should be done

in such a way that the triple bond gets

the lowest possible number. It's

important to note that the location of

the triple bond is more important than

the position of any branches or

substituents when assigning numbers. For

instance, if the triple bond is on the

second carbon, numbering should start

from the end of the chain closest to the

triple bond. Even if it means the branch

gets a higher number. Let's look at an

example to clarify. If the triple bond

is on the second carbon and the branch

is further down the chain, numbering

will start from the end nearest to the

triple bond to give it the smallest

possible number. Rule three, how to name

the parent chain having a triple bond.

If the parent chain does not contain any

substituents or branches, the name

should reflect the position of the

triple bond followed by the total number

of carbons in the chain and ending with

Y ne to indicate the presence of a

triple bond. For example, consider a

structure with five carbons in the main

chain and a triple bond present at the

second carbon. The name of this compound

will be two pentine. Rule four. How to

name a branched chain structure having a

triple bond. When a triple bond is

present along with branches, the

position and name of the branches or

substituents must be mentioned at the

beginning of the compound's name. It's

essential to prioritize the triple bond

when numbering, ensuring that it gets

the smallest possible number. Let's take

an example. If a methyl group is

attached to the third carbon and a

triple bond is located on the second

carbon, the name of this compound will

be threemethyl 2 butine. Rule five. How

to name multiple branches in a chain

with a triple bond. If the parent chain

has identical branches, prefixes like

die, try and tetra are used to indicate

the number of branches. If there are

different types of branches, they are

arranged in alphabetical order when

naming the compound. Consider this

structure. The parent chain has a triple

bond on the first carbon, two methyl

groups on the third carbon, and an ethyl

group on the fourth carbon. Since the

branches are different, we follow the

alphabetical order. The name of this

compound will be four ethyl 33 dmethyl

1hexene. Rule six, how to name compounds

with more than one triple bond. If a

compound has multiple triple bonds,

prefixes like diion for two triple

bonds, triion for three triple bonds and

so on are used. Additionally, the

positions of all triple bonds must be

indicated in the name. There are some

special cases when both double and

triple bond are present in the parent

chain. Then we should prefer the double

bond and numbering will start from that

side which gives least number to double

bond and also need to prefer double bond

in naming also. Let's take the following

structure to make it clear. It has

double bond and second carbon and triple

bond at fifth carbon. So its name will

be two hexene 5 ion. I hope this video

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any confusion, let me know if it

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