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