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Figure 3
Examples of counting π electrons in sulfur–nitrogen rings where all atoms are sp2-hybridized. The total numbers of π electrons are (a) six (Wilberg et al., 2001BB54), (b) six (Chivers & Manners, 2009BB8), (c) six (Chivers & Manners, 2009BB8), (d) ten (Chivers & Manners, 2009BB8), (e) eight (Chivers, 2005BB7), (f) ten (Chivers, 2005BB7) and (g) ten (Chivers, 2005BB7). All rings apart from (e) obey Hückel's 4n + 2 rule, where n is an integer. Therefore, all rings apart from that in (e) are perceived as aromatic rings.

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