Why 2,2-dimethylpropane is not called isopentane?

why 2,2-dimethylpropane is not called isopentane? since 2-methylpropane is called isobutane




In common nomenclature, the prefix 'iso-' is applied when the chain of carbons is continuous bar one methyl group. The example you provided, 2-methylpropane, is observed to be continuous with exception to one methyl group bound to the central carbon atom. 


However, 2,2-dimethylpropane does not feature an analogous structure: because two methyl groups are bound to the central carbon, the same classification is inapplicable. In place, the molecule could be labelled as 'neopentane', in which the prefix specifies a continuous chain excepting two alkyl groups.


[![Isopentane](https://i.stack.imgur.com/qYImH.png)](https://i.stack.imgur.com/qYImH.png)


The above image is 2-methylbutane, or isopentane. 


[![Neopentane](https://i.stack.imgur.com/WSoFt.png)](https://i.stack.imgur.com/WSoFt.png)


The above-shown image is 2,2-dimethylpropane, or neopentane


If you desire further information concerning the nomenclature, I would advise the following link, from which these images were extracted: <http://www.chem.ucla.edu/~harding/IGOC/C/common_name.html> 


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