How may trichloro derivatives (only constitutional isomers) of propane `(C_3H_5Cl_3)` are possible?

Options

A. Six
B. four
C. Five
D. Seven

Answer

C

Explanation

In propane, `C-1` and `C-3` are identical. All three Cl's are placed on the terminal carbon:
`underset(1,1,1-"trichloropropane")(overset(3)(C)H_(3)overset(2)(C)H_(2)overset(1)(C)Cl)` Two Cl's are placed on the terminal carbon and the third Cl either on the middle carbon or on the other terminal carbon:
`underset(1,1,2-"Trichloropropane")(overset(3)(C)H_(3)overset(2)(C)HCloverset(1)(C)HCl_(2))" "underset(1,2,3-"Trichlorpropane")(Cloverset(3)(C)H_(2)overset(2)(C)H_(2)overset(1)(C)HCl_(2))`
One Cl on one of the terminal C's and the two Cl's on the middle carbon:
`underset(1,2,2-"Trichloropropane")(overset(3)(C)H_(3)overset(2)(C)Cl_(2)overset(1)(C)H_(2)Cl)` One Cl on each carbon atom:
`underset(1,2,3-"Trichlropropane")(Cloverset(3)(C)H_(2)overset(2)(C)HCloverset(1)(C)H_(2)Cl)`