Carbanion Rearrangements. Collision-Induced Dissociations of the Enolate Ion of Heptan-4-one

Article abstract of DOI:10.1021/ja00274a005

The mechanisms of formation of the major negative ions produced in the collision-induced fragmentations of the enolate ion of heptan-4-one have been studied by using a series of D- and 13C-labeled compounds.H atom loss is specific, involving position 3 (relative to the enolate position, 5).Methane elimination, the most abundant collision-generated fragment ion, largely involves the 1(7)CH3 group together with a hydrogen atom from C-3(5).It was concluded from 13C and D isotope effects that this reaction is stepwise with two kinetically significant steps.A minor methane loss (ca. 10percent) involves H from C-6(2).C2H4 loss is also an important process, occurring for the most part (>90percent) by loss of the ethyl group with a concomitant γ-hydrogen transfer to the anionic carbon or to oxygen, producing the CH3CH2CH2COCH2^- and CH3CH2CHC(OH)CH2^- anions.Again, isotope effects show that the reaction must be stepwise.An unusual minor C2H4 loss is also observed involving specifically the elimination of a C2, C3 ethene unit, a reaction which must involve a methyl migration.Other decompositions are as follows: Loss of H2 proceeds by two mechanisms, the first involving the 5 and 6 positions and the second the 1 and 2 positions.Elimination of C2H5^. is specific, producing ^.CH2COCH^-C2H5.Loss of C3H8 occurs by two mechanisms, viz., loss of C3H7 from positions 5, 6, and 7 together with a hydrogen from position 3, with the second loss involving the methyl and ethyl groups at positions 1 and 6, 7, respectively.