ACE's Heuristic Mechanism Rules

Mechanism rule Parameter Automatic feedback?
General chemical rules
No SN2 at sp- or sp2-hybridized atom. no
No ionization of sp- or sp2-hybridized atom. no
No 1° carbocations. no
Violation of pKa rule [(best base's conjugate acid pKa – best acid pKa) ≤ 8]. flags bits 0–1 = "do not consider first step", "do not consider last step" no
No even-electron pericyclic reactions. no
No four-atom pericyclic reactions. no
Cationic shifts must be 1,2-shifts. no
No zwitterions. flags bit 2 = "consider only positive atoms bearing H" no
No multiply charged atoms. no
No multiply charged molecules. no
No charged molecules of same sign reacting with one another. flags bit 3 = "allow proton transfers" no
No X–H bond acts as a nucleophile. no
No four-membered transition states for H+ transfer. no
No termolecular steps. no
No dyotropic rearrangements (A–B–C–D → D–B–C–A). no
No σ-bond metatheses or dyotropic rearrangements. no
Reaction-condition-specific rules
No radicals under polar conditions. no
No acids under these basic conditions should have pKa < n. (The response may show the acids explicitly or may produce them in a mechanistic step but omit them from the drawing.) pKvalue yes
No bases under these acidic conditions should have pKb > n (conjugate acids whose pKa > n). (The response may show the bases explicitly or may produce them in a mechanistic step but omit them from the drawing.) pKvalue yes
No SN2 under acidic conditions. no
No carbocations under basic conditions. no
Mechanism-drawing conventions
No atom should receive and supply electrons simultaneously. no
No resonance arrow where there should be one. flags bit 0 = "do not consider first step" no
Resonance arrow where there shouldn't be one. flags bit 0 = "do not consider first step" no