H-Shifts in Conjugated System Tautomerization

[ieva-jonusaite]

Requirement

The system shall identify a substructure that matches the general configuration:
H–A–(...)–D

Where:

• A and D are terminal heteroatoms from the specific list: Oxygen (O), Nitrogen (N), Sulfur (S), Selenium (Se), or Tellurium (Te).
• (...) represents a conjugated system. For the purpose of this rule, a conjugated system is a continuous, unbroken pathway of atoms that allows for electron delocalization. This pathway is formed by either:
  • A sequence of alternating single and double bonds between carbon atoms.
  • A lone pair of electrons on a heteroatom (N, S, Se, Te, or O⁺) that is adjacent to a double bond in the alternating single-double carbon bond sequence.

Upon identifying a structure that meets these conditions, the system shall allow for the bidirectional interconversion to its corresponding tautomer, A=(...)=D–H.

This transformation involves a coordinated rearrangement of the bonds within the conjugated path (...).

This enables proton shifts over distances, such as 1,3-, 1,5-, 1,7-, 1,9-, 1,11-, 1,13-, 1,15-, 1,17-, and 1,19-shifts.

---

Background

This requirement describes the tautomeric migration of a hydrogen atom between two distant heteroatoms. This long-range shift is possible because the conjugated system provides a continuous electronic pathway for the bonds to rearrange.
In both cases, the ability of electrons to delocalize (or move) along this path stabilizes the transition, allowing the proton to migrate.

---

Examples

• 1,3 Shift (Rule No PT_06_00)

• 1,5 Shift (Rule No PT_07_00)

• 1,7 Shift (Rule No PT_09_00)

• 1,9 Shift (Rule No PT_10_00)

• 1,11 Shift (Rule No PT_11_00)

• 1,13 Shift (Rule No PT_11_01)

• 1,15 Shift (Rule No PT_11_02)

• 1,17 Shift (Rule No PT_11_03)

• 1,19 Shift (Rule No PT_11_04)