Branched hydrocarbons: For branched hydrocarbons, IUPAC rules dictate that the longest continuous carbon chain be identified as the root, with branching groups named as alkyl substituents. An alkyl group can be considered as an alkane from which one hydrogen has been removed; the name is derived by replacing the suffix -ane with –yl. Thus, CH 3 is a methyl group, C 2 H 5 an ethyl group, and so forth. The position along the main carbon chain where an alkyl group is attached is designated by a number. The numbering of carbon atoms in the chain starts at the end closest to where the substituent is attached so that the lower of two possible numbers can be assigned to that position. The presence of more than one alkyl group along a carbon chain is indicated by a Greek prefix (di-, tri-, tetra-, penta-, etc., for 2,3,4,5 alkyl substituents). In this case, each alkyl group must be assigned a number (as low as possible) to indicate its position.