Final answer:
Numbers are assigned to each carbon atom in the parent chain of an alkane to give the lowest possible numbers to the substituents, ensuring a systematic naming that distinguishes between isomers.
Step-by-step explanation:
When assigning numbers to each carbon (C) atom in the parent chain of an alkane, the primary criterion is to ensure that the substituents attached to the chain receive the lowest possible numbers. First, you identify the longest continuous chain of carbon atoms, which becomes the parent chain. Then, number the carbon atoms starting at the end closest to the first substituent group. The numbering should minimize the numerical position of the branches.
For example, if numbering from one end of the chain results in substituents on the 3rd and 5th carbons, while numbering from the other end puts them on the 4th and 6th, the first method is used to assign lower numbers to the substituents. It's also important to remember when naming an alkane: if the same substituent occurs multiple times, this is indicated with Greek prefixes like di-, tri-, and tetra-, which are placed before the substituent's name without affecting alphabetical order.
Overall, the goal is to provide a clear and systematic way to distinguish between possible isomers of the alkane, ensuring that each unique structure receives a unique name.