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16.6 All of these compounds have filled HOMOs, so they are all aromatic. b) c) d) E 0 16.7 According to Huckel's rule, aromatic compounds are cyclic, fully conjugated, planar, and have (4n+2) TT electrons. Antiaromatic compounds are cyclic, fully conjugated, planar, and have 4n TT electrons. a) 4 TT electrons, antiaromatic b) 6 TT electrons, aromatic c) 10 TT electrons, aromatic if planar d) 2 TT electrons, aromatic 16.8 a) 6 TT electrons, aromatic (do not count pairs on N's) b) 6 TT electrons, aromatic (count one pair on O) c) 6 TT electrons, aromatic (count one pair on S) d) 6 TT electrons, aromatic (count one pair on O) e) 6 TT electrons, aromatic (do not count pairs on N's) f) 8 TT electrons, antiaromatic (count pair on N) 6 16.9 5 7 4 8 3 9 2 10 The bond between C-9 and C-10 is the shortest because it is a double bond in four of the five resonance structures. 239