Interpretation of Electron Impact Mass Spectra Fragmentation mechanisms

Interpretation of Electron Impact Mass Spectra - Fragmentation mechanisms and rules Lecture 2 2015 in Applied Spectrocopy Torben Lund RUC

Electron impact ionization (EI) ABC + e- ABC+. + 70 e. V e- + e- Molecular ion (1 e. V) 55 e. V + ABC+. AB+ + C. ABC+. A. + BC+ AB+ A + B+ 0. 1 e. V Mass spectrum

Ionization mechanisms in EI mass spectrometry Four mechanisms: s a i r. H

s - cleavage

a-cleavage

r. H : Mc. Lafferty rearangement

EI-Mass Spectra of different functional groups • • Alkenes Alkyl substituted aromatic compounds Alcohols Aldehydes Ketones Carboxylic acids Esters Amines

Alkenes: m/z =41

Alkyl benzenes

Alkylbenzenes

Alcohols (R-OH): M-18, Loss of alkyl groups

Alchohols

Alchohols: Loss of alkyl group, M-18

Phenols: M-1, M-28, M-29

Aromatic aldehydes: M-1, M-29 Alifatic aldehydes: m/z = 29, M-43

Alifatic Ketones: M-15, M-29, M-43, m/z = 58, 72, 86

Ketones (1)

Aromatic ketones: m/z =105, 120

Methyl Esters: M-31, m/z =59, 74

Esters

Carboxylic Acids: M-17, M-45, m/z = 45, 60

Interpretation of Electron Impact Mass Spectra - Fragmentation mechanisms and rules Lecture 3 2015 in Applied Spectrocopy Torben Lund RUC

Amines: Nitrogen rule obeyed, a-cleavage, m/z = 30

Alkylamines

Aromatic Amines

Nitriles, R-CN

Nitro compounds

Halides, R-X , X = Cl, Br, I

Halides, X = Cl and Br

Ethers

Pavia 10 c

Problem 6 p. 126 Yellow problembook

Problem 8 p 128

b-cleavage