Isomerism

Organic compounds are capable of being arranged in different ways.  Organic compounds with the same molecular formula but different arrangements are called isomers. Hydrocarbons exhibit isomers when there are 4 or more carbons in the chain.

Let’s look at 2 isomers butane and methyl propane.

The molecular structure for both butane and methyl propane is C4H8 . If you count the number of carbon and hydrogen atoms you will see that they both posses 4 carbon and 8 hydrogen atoms.

You may be wondering if methyl propane is an Alkane. Well let us look at it. Does it follow the general formula CnH2n+2 ?

Well from examination we will see that it does and that it contains only carbon-hydrogen bonds, this means that it is an Alkane. The only difference between butane and methyl propane is that methyl propane possesses a branch in its carbon chain where as butane has a straight chain.

This difference is also the reason for the difference in names between the 2 molecules. When naming branched hydrocarbons we:

1)      Count the longest consecutive carbon chain. This chain will be the parent chain.

2)      Identify the branch chain. The branch will be the part of the chain that branches from the parent chain, hence the name branch.

In the case of methyl propane, the longest consecutive chain is 3 carbons long.  The branch group only possesses one carbon hence it is called the methyl group. Remember the prefix – meth means one carbon.  Please note that branched groups ends with the suffix – yl.

We also state the name of the branch before the parent chain, hence methyl propane.

Take a look at the compound below:

The longest consecutive chain of carbon atoms is 6 carbons long. You might have thought that the longest chain is 4 carbons long. This is not the case because even if the chain is bent, it is still a consecutive chain of carbons and in naming the compound we use the longest consecutive chain as the parent chain.

The name of this compound is methyl hexane.

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