1.2 Cyclic Systems
23
~~-------- ~-------)
y
correct
incorrect
\~------~ ~------~)
y
correct
incorrect
correct
incorrect
The numbering starts at the most counterclockwise non-fused C atom of
the uppermost ring positioned farthest to the right and proceeds clockwise around the periphery of the whole structure. Carbon atoms common
to more than one ring are numbered indirectly by attaching the letters a,
b, c, etc. to the locant of the preceding C atom. Until now interior C atoms
were numbered in the same manner starting from the highest locant of the
periphery and proceeding clockwise towards the center of the structure.