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Steps for naming branched chain hydrocarbons:

Step 1

Only the longest chain of carbon atoms in the compound is considered. It is named according to its components.

Step 2

  • We name the branches separately.
  • The longest chain can have Alkyl groups, Functional groups, halogens, etc. attached to it.
  • The Branch name and its position is noted.
  • The position of the Alkyl group is determined from the side that gives the position closest to the first carbon (the smallest number).

Step 3

(Prefix + suffix) of longest chain + branch name and its position= Compound Name

 

Let’s look at a few examples to understand this better:

Naming of 2 Methyl Propane (also called Isobutane)

Step 1

The Longest chain of carbon atom is named first

  • The compound contains 3 Carbon atoms as longest chain
  • We use 'Prop' for 3 

Since it is an alkane, we get Propane

LONGEST CHAIN OF 2-METHYL PROPANE - Teachoo.jpg

Step 2

We name the branches separately

  • The branch is CH 3 .
  • It is an alkyl of 1 carbon atom

Hence we name it Methyl.

ONE CH3 GROUP FORMING A BRANCH - Teachoo.jpg

Step 3

  • Now we check the number where the branch is attached.
  • it is attached to the second carbon , as we count from both sides.

So the smallest position is 2 .

NUMBERING OF LONGEST CHAIN - Teachoo.jpg

Step 4

  • We combine the data we’ve noted so far into a name.

(Prefix ‘prop’ + suffix ‘ane’ ) + 2 Methyl = 2-Methyl Propane

 

Naming of 2 - Methyl Butane (also called Isopentane)

Step 1

Longest chain of carbon atoms is named first.

  • The compound contains 4 Carbon atoms in longest chain

We use 'But' for 4 and it is an alkane, so we get Butane

LONGEST CHAIN OF 2-METHYL BUTANE - Teachoo.jpg

Step 2

We name the branch separately

  • Since branch is CH 3

It is an alkyl of 1 carbon atom- called Methyl

ONE CH3 GROUP FORMING A BRANCH. - Teachoo.jpg

Step 3

We check the carbon number where the branch is attached

It is attached at second number from left side and third number from right side, we take lowest of possible positions 2 and 3 i.e. 2

NUMBERING OF LONGEST CHAIN. - Teachoo.jpg

Step 4

Combining Names

(Prefix ‘but’ + suffix ‘ane’) + 2 Methyl= 2-Methyl Butane

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Maninder Singh

CA Maninder Singh is a Chartered Accountant for the past 12 years and a teacher from the past 16 years. He teaches Science, Economics, Accounting and English at Teachoo