The bolded formula is the original formula, above is the formula with one fewer degree of unsaturation (it is more hydrogenated), while below is formula with one more degree of unsaturation (dehydrogenated). On the left is the homologue with one fewer methylene (-CH2- unit), while on the right is the formula with one more methylene. If the molecular formula contains any heteroatoms (only nitrogen, oxygen, and sulfur are currently supported), bottom part are formulas that differ by one fewer and one more of any one heteroatom that is contains.
