Prefix iso is used for those alkanes in which one methyl group is attached to the next to end carbon atom (second last) of the continuous chain. Example isopentane is CH3CH(CH3) - CH2CH3 Prefix neo is used for those alkanes in which two methyl groups are attached to the next to end carbon atom (second last) of the continuous chain. Example neopentane is CH3C(CH3)2 - CH3 Prefix sec- is used for those carbon atoms which are joined to two other carbon atoms. Example I CH3 -CH-CH3 Prefix tert- is used for those carbon atoms which are joined to three other carbon atoms. Example I CH3 -C-CH3 I CH3 iso and neo are basically used for alkyl groups and sec and tert are used for carbon atoms which have functional groups, charge or are radicals.