What is the IUPAC name for the insecticide, #"DDT"#?

The old name used to be 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane, which was shortened to DichloroDiphenylTrichloroethane and then to DDT.

The parent name in that system was "ethane".

The IUPAC name

The most recent IUPAC rules state that we choose as parent structures the longest groups that are symmetrically linked to other groups.

Thus, in this molecule, the parent structures are the 4-chlorophenyl rings and the linking bonds are in the #"Cl"_3"CCH="#.

The parts of the name are generated in order:

(a) The locating numbers on the parent groups where the linking bonds are
attached: 1,1'.

(b) The name of the linking group: 2,2,2-trichloroethane-1,1-diyl

(c) The numerical prefix before the name of the parent groups: bis.

(d) The name of one parent group enclosed in parentheses: (4-chlorobenzene).

Put them all together and you get the IUPAC name:

1,1'-(2,2,2-trichloroethane-1,1-diyl)bis(4-chlorobenzene)