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