Mass spectrometry in structural and stereochemical problems-XCVII

Intramolecular hydrogen transfer in mass spectra. II. McLafferty rearrangement and related reactions

“…It may also be noted that a small portion (around 7%) of the rearrangement ions is not due to McLafferty rearrangement but rather to methyl migration. 137 Aliphatic semicarbazones also show abundant ions due to McLafferty rearrangement. In the case of n-valeraldehyde semicarbazone, the McLafferty rearrangement ion forms the base peak in the spectrum,138 while for the di-n-butyl semicarbazone the ions for both double and single McLafferty rearrangement are prominent.138 In this case, the type of hydrogens abstracted does play a role in the rearrangement, secondary hydrogens being abstracted in preference to primary ones.138 A second rearrangement of semicarbazones involves the loss of HCNO from the molecular ion.…”

Studies of the synthesis of 5-hydroxy 6-keto steroids and related 6-keto steroids

“…In the mass spectrum of 51, a relatively abundant ion (40%) at m / z 383 is assigned to an ion formed by loss of an oxygen atom from the molecular ion. This type of fragmentation has been observed in the mass spectrum of cyclohexanone oxime (50). The structural assignment 51 was confirmed by treatment of the product with sodium bisulfite in aqueous ethanol to give the 3a,5a-cyclo ketone 52 (5 1).…”

Mass Spectrometry in Structural and Stereochemical Problems. CCXVII. Electron Impact Promoted Fragmentation of O-Methyl Oximes of some α,β-Unsaturated Ketones and Methyl Substituted Cyclohexanones

“…The remaining source of extruded ethylene could be explained by fl-fission of the molecular ion (see 8 -+s, mle 113) followed by homolytic fission of the C,-C, bond. This process has analogy with that found to operate in the extrusion of ethylene from cyclohexanone oxime (4).…”