title: A modified McLafferty rearrangement in the electron impact mass spectra of dansylated amino-acid methyl esters.
abstract: Electron impact mass spectra of dansylated amino-acids and their methyl esters show a very time intense peak at m/z 171. A systematic study failed to show the genesis and origin of this ion. The present work is devoted to the electron impact mass spectrometric (EIMS) analysis of the appearance of this ion m/z 171 in the spectra of dansylated amino-acid methyl esters and its diagnostic importance in the analysis of dansyl derivatives. A structural model for this study is offered by a series of N-alkylated aromatic sulphonamides. The EIMS spectra of these compounds indicate that the classic fragmentation is accompanied by hydrogen migration from aliphatic radicals to the aromatic ring in a manner analogous with dansylated amino-acids. A modified McLafferty rearrangement mechanism is proposed for this EI reaction. The metastable transitions and the deuterium-labelled compounds confirm this mechanism and the origin of the itinerant hydrogen.
authors.affiliation: Department of Analytical Chemistry, Faculty of Pharmacy, University of Medicine and Pharmacy Iuliu Hatieganu, Cluj-Napoca, Romania.
authors.forename: R
authors.initials: R
authors.lastname: Oprean
authors.forename: L
authors.initials: L
authors.lastname: Roman
authors.forename: R
authors.initials: R
authors.lastname: Sandulescu
mesh_terms: D000596:Amino Acids / Q000737:chemistry*; D003619:Dansyl Compounds / Q000737:chemistry*; D003903:Deuterium; D004952:Esters / Q000737:chemistry; D007553:Isotope Labeling; D013058:Mass Spectrometry; D013449:Sulfonamides / Q000737:chemistry
chemical_list: D000596:Amino Acids; D003619:Dansyl Compounds; D004952:Esters; D013449:Sulfonamides; D003903:Deuterium