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Stereoisomeric fragment ions arising from decomposition of enol cation radicals of different internal energy content
Author(s) -
Weiske Thomas,
Halim Herman,
Schwarz Helmut
Publication year - 1984
Publication title -
organic mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0030-493X
DOI - 10.1002/oms.1210191206
Subject(s) - chemistry , mndo , radical , ion , bond cleavage , enol , dissociation (chemistry) , decomposition , mass spectrum , isopropyl , medicinal chemistry , computational chemistry , stereochemistry , photochemistry , organic chemistry , molecule , catalysis
The 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.