new index atom name original index 1 C 10 2 C 12 3 C 11 4 C 13 5 C 14 6 C 16 7 C 15 8 C 17 9 C 7 10 C 8 11 C 18 12 C 19 13 C 6 14 C 9 15 Cl 4 16 Cl 5 17 Cl 1 18 Cl 2 19 Cl 3 20 H 21 21 H 23 22 H 22 23 H 24 24 H 25 25 H 27 26 H 26 27 H 28 28 H 20