Journal of the American Chemical Society p. 3888 - 3893 (1986)
Update date:2022-08-05
Topics:
Stringer, Michael B.
Bowie, John H.
Holmes, John L.
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.
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