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