Abstract
AbstractThe least‐squares analysis of collisional activation mass spectra provides evidence that 1,1‐dihydroxy‐3‐methylbutene cation radical (a) and 1‐hydroxy‐1‐methoxy‐3‐methylbutene cation radical (c) (generated in a McLafferty‐type rearrangement from 2‐isopropyl‐3‐methylbutanoic acid and its methyl ester) give rise to product ions b and d, the stereochemistry of which at the double bond is determined by the lifetime (internal energy) of a and c, respectively. Decompositions of a and c in the ion source yield predominantly the less stable cis‐configurated stereoisomers of b and d, whereas dissociation of a and c at longer lifetimes (lower internal energy) results in the formation of the thermochemically more stable trans isomers of b and d. A qualitative MNDO analysis is provided which takes into account the special features of stereoelectronic control of radical chemistry in the cleavage of a carboncarbon bond.
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