HAA and 3FO Formation Pathways. The major pathways forming HAA also involve either 3-hexulose or HEH as an intermediate. Starting from 3-hexulose, HAA is formed through a one-step retro-aldol reaction, with ∆G of 31.10 kcal/mol. Starting from HEH, the pathway to HAA diverges from the pathways to HMF and FF at species 6-4 (denoted as 3-DGE). Competing with the 1,4-conjugated elimination, a cyclization reaction with similar activation energy can occur on 3-DGE, resulting in the formation of a 5-membered ring (7-1). This species can undergo a surprising single-step reaction that produces HAA and 3-Furanol via a 1,4-conjugated elimination coupled with a β-elimination (Fig. ). From here, 3-Furanol can be converted into the more stable 3-(2H)-furanone (3FO) through a double-water catalyzed keto-enol tautomerization reaction with ∆G = 18.60 kcal/mol (Fig. ). It is thus observed that the overall barriers to the formation of HAA and 3FO via the HEH-pathway are both 30.98 kcal/mol.