84959-41-1Relevant academic research and scientific papers
Comportement sous impact electronique des dihydro-2,3 4H-pyrannes: isomerisation des ions moleculaires avant fragmentation
Sarraf, Marcel,Audier, Henri,Morizur, Jean-Pierre
, p. 78 - 82 (2007/10/02)
Studies of electron impact (EI) mass spectra of some 2-substituted-2,3-dihydro-4H-pyrans demonstrated the occurence of a specific rearrangement of the molecular ion prior to fragmentation.Mass spectra of three carbonyl derivatives were examined: 2-acetyl-6-methyl-2,3-dihydro-4H-pyran, 2-propionyl6-methyl-2,3-dihydro-4H-pyran, and 2-valeryl-6-methyl-2,3-dihydro-4H-pyran.Deuterium-labelling showed this rearrangement to be favoured at reduced internal energy.It may lead to another dihydropyran isomer after cleavage of the O-(C-2) bond of the heterocycle.The Mike-spectra T0.5 values and appearence energy measurements confirmed this proposition. 2,3-Dihydro-4H-pyrans substituted by a vinyl group at C-2 underwent the same rearrangement. 2-Vinyl-2,3-dihydro-4H-pyran and cyclohex-3-ene-1-carboxaldehyde showed identical Mike-spectra and T0.5 values.This mechanism makes it possible to explain the intense peaks at (M-CHO.)(+) and (M-C2H3O.)(+) respectively observed in the mass spectra of 2-isopropenyl-2,3-dihydro-4H-pyran and 2-isopropenyl-6-methyl-2,3-dihydro-4H-pyran.The Mike-spectra of the ions (m-29) and (M-43) were compared with the Mike -spectrum of the ion (M-H) of 1-methyl-1-cyclohexene, and T0.5 values measured for the principal transitions found to be identical.The syntheses of the different products were reported.
