1。 The longest C chain (the one with the most C) in the selected molecules is the main chain, and there are several C atoms in the main chain, which are several alkanes. For example, C-C-C-C-C-C is hexane (a, b, c, d, e, f, g, n).

2。 Starting from the end of the main chain closest to the branch, the C atoms in the main chain are numbered. For example:

Carbon-carbon-carbon-carbon

1 2 3 4

3。 Take the branched chain as the substituent, write the name of the substituent (such as methyl -CH4, ethyl -CH2-CH4) before "several alkanes", write the number corresponding to the C atom of the main chain to which the substituent is connected, and separate it from the text with a dash "-". For example:

Carbon-carbon-carbon-carbon

1 2 3 4

2- methylbutane, when there is a methyl group in the 2- position;

When ..

1 2 3 4

When there are two methyl groups in position 2, it is 2- dimethylbutane;

When ..

1 2 3 4

2,3- dimethylbutane, when there are methyl groups in the 2-position and 3-position.