Branches of aromatic groups

Additional ways of indicating the presence of a phenyl group include Ph, CgHr, and 0. 

Some aromatic group names plus the benzyl group. 

Up to this point, this chapter has discussed aromatic systems composed exclusively of rings of carbon atoms. But aromatic systems can contain heteroatoms, which in this case means any atoms in the ring other than carbon. 

Heteroatoms (such as O, S, N) that are double-bonded to other atoms in a ring can t donate lone-pair electrons to the pi system because their p-electrons are already involved in the double bond. Single-bonded heteroatoms can donate a single lone-pair to the pi system but not two, because one lone-pair must be in an unhybridized p orbital orthogonal (at 90 degrees) to the sp ring plane. 

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