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