Tautomers strict mode

[even1024]

Background

The current tautomer matching logic controls which atoms can participate in tautomerism via indigoSetTautomerRule. However, these rules primarily define topological connectivity limits and do not validate the chemical environment or "activation" required for such transformations. This leads to False Positives where tautomerism is topologically possible but chemically invalid, such as unactivated hydrocarbon shifts.

Solution

Introduced aSTRICT keyword for Tautomer matching (e.g., "TAU STRICT").
This mode serves as an additional validation layer. When enabled, it strictly enforces that any Carbon atom participating in a tautomeric shift must be chemically activated by an electron-withdrawing Heteroatom (O, N, S, P).

Rules

The validation logic uses a Depth-First Search (DFS) trace to verify the electronic path:

1. Direct Activation:
   The Carbon atom is directly bonded to an activating Heteroatom (O, N, S, P). (Path length = 1 bond).

   • Applies to: Enols (C=C-OH), Imines.

2. Conjugated (Vinylogous) Activation:
   The Carbon atom is connected to an activating Heteroatom (O, N, S, P) through a continuous path of alternating bonds (Single $\leftrightarrow$ Double/Triple).

   • Mechanism: The alternating $\pi$-system acts as a conductive wire, allowing the Heteroatom's electron-withdrawing effect to transmit to distant carbons ($\gamma, \epsilon$ positions).

Examples & Logic Table

Case Name	Structure Example	Status	Reason
Standard Keto	H-C-C=O	PASS	Valid. Path is Single $\to$ Double $\to$ O. Effect reaches carbon.
Enol	C=C-OH	PASS	Valid. Direct connection to Oxygen.
Vinylogous	H-C-C=C-C=O	PASS	Valid. Alternating bonds transmit activation to distal carbon.
Aromatic	H-C-Ph-C=O	PASS	Valid. Aromatic ring conducts resonance effect.
Hydrocarbon	C-C=C-C	FAIL	Invalid. No Heteroatom anchor. Pure alkyl shift.
Broken Path	O=C-CH2-CH=C	FAIL	Invalid. Path broken by sp3 (-CH2-) linkage. Resonance cut.
Isolated Ether	O-CH2-CH=C	FAIL	Invalid. Oxygen isolated by single bonds. No resonance interaction.

Technical Implementation

• Logic: Implemented TautomerMatcher::isTautomerActivatedCarbon using the trace algorithm.
• Flags: Updated parseConditions to interpret TAU STRICT correctly.