ome common branched alkyl groups are: 2rmostogmegtmemaameaem89gnl2 dditional prefixes are also used:sec-(ors)fo ndary,and ot-0- s-Mot chain in the i: ethe maln chn 66 An alkyl group is formed by removing a hydrogen from an alkane. It is named by removing the –ane suffix and replacing it by –yl. CH3- methyl; CH3CH2- ethyl; CH3CH2CH2- propyl Additional prefixes are also used: sec- (or s-) for secondary, and tert- (or t-) for tertiary. A secondary carbon is directly attached to two other carbons. A tertiary carbon is directly attached to three other carbons. Some common branched alkyl groups are: For systematically naming branched alkanes, four IUPAC rules are used: IUPAC RULE 1: Find the longest chain (stem) in the molecule and name it. Groups other than hydrogen attached to this chain are called substituents. If the molecule has two or more stems of equal length, the one with the most substituents is the base stem chain. IUPAC RULE 2: Name all groups attached to the longest chain as alkyl substituents. If a substituents chain is branched, find the longest chain in the substituents and then name all of its substituents. IUPAC RULE 3: Number the carbons of the longest chain beginning with the end closest to a substituents. If there are two substituents at equal distance from the ends of the chain, assign the lower number to the substituents coming first in alphabetical order. If there are three or more substituents, the chain is numbered to give the lower number at the first difference between the two possible numbering schemes (first point of difference principle). Substituents are numbered outward from the main chain. C1 will be the carbon attached to the main stem