Question

Question #ce86c

Answer 1

Think of the ethane molecule as two carbon-atoms surrounded by hydrogens, being replaced one by one.

Explanation:

For the first `Cl` there is only one possibility. Of course you can replace any of the six `H`'s, but they are all equivalent, so it doesn't matter which you choose (result: chloro-ethane)

For the second you can choose to use the `C` that already has the first `Cl`, or you can choose the other (result: either 1,1- or 1,2- dichloro-ethane).

For the third : if you start with the 1,1 version you can add on that `C`, or on the other (1,1,1- or 1,1,2- trichlorothane). if you start with the other, it doesn't matter, because 1,2,2 is automatically renamed to 1,1,2.

In short, if there is a majority on one of the `C`'s, they get the lowest number.

You should be able to work it out from here.