Abstract: Semiempirical molecular orbital calculations on the unimolecular massspectrometric fragmentation of tetrahydroimidazole-substituted methylene β-diketones are carried outby Austin Model 1 method, and the calculated results give a strong support to ourexperimental results reported previously. The optimum of the investigated molecular configurationindicates that the two hydrogen atoms attached to nitrogen atom have different activities dueto their chemical environment; the relative energies of the ions in fragmentation pathway ofionized tetrahydroimidazole-substituted methylene β-diketones provide indirectly an evidencefor both the existence of ion/neutral complex and the stabilities of these ions.

Key words: Semiempirical AM1 calculation, Ion/neutral complex, Tetrahydroimidazole-subsubstituted methylene β-diketone