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