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Table 2 Tautomerism patterns detected by InChI

From: InChI, the IUPAC International Chemical Identifier

M = Q  ZH ↔ MH  Q = Z or M = Q  Z ↔ M Q = Z

M, Z = NIII, OII, SII, SeII, TeII (Roman superscripts designate chemical valence)

Q = C, N, S, P, Sb, As, Se, Te, Br, Cl, I

H = hydrogen, deuterium, or tritium

The “=” bond may be a double bond, a bond in the alternating single/double bond ring, or a “tautomeric” bond (shown in blue)

The H atom below can be replaced with a negative charge