Since the 1913 edition of Webster's dictionary, the nomenclature of hydrocarbons has become more specific in regards to structure. Butane is now specifically a string of four linked carbon atoms, like so:
H H H H
| | | |
H-C-C-C-C-H
| | | |
H H H H
The other form of C4H10 is no longer considered a butane, but instead it is identified as 2-
methyl-
propane, as that is its longest string of carbon atoms:
H H H
| | |
H-C-C-C-H
| | |
H | H
H-C-H
|
H