1. Mechanism of “Oxygen rearrangement”
in mass spectrometry
Nino Todua, Karl K. Irikura, Stephen E. Stein and Anzor Mikaia
National Institute of Standards & Technology, Gaithersburg, MD , USA

2. NIST - National Institute of Standards & Technology
NIST/NIH/EPA Mass Spectral Library
NIST - National Institute of Standards & Technology
NIH – National Institute of Health
EPA – Environmental Protection Agency

3. A Mechanism For the Formation of
N-Methylpentafluoroethylnitrilium Cation
C. R. Clark, J. DeRuiter, A. K. Valaer, F. T. Noggle, Journal of Chromatographic Science, 1995, 33,p

4. CH3 – N+ ≡ C – C3F7 CD3 – N+ ≡ C – C3F7
Mass Spectra of Heptafluorobutyryl (HFB) Derivatives of
Metamphetamine and Ecstasy, and their D4-analogs
F. T. Peters, S Schaefer, R. F. Staack, T. Kraemer, H. H. Maurer,
Journal of Mass Spectrometry, 2003, 38,
CH3 – N+ ≡ C – C3F7 CD3 – N+ ≡ C – C3F7
m/z m/z 213

5. Mass Spectra of Methylated Sulfabenzamides

6. Mass Spectrum of Sulfabenzamide
S. Meyerson, H. Drews, E. K. Fields,
Analytical Chemistry, 1964, 36,

7. Quantum Chemistry Methods
Candidate mechanisms from chemical intuition or PM6 isopotential searching.
B3LYP/6-31G(d) to estimate energetics (±20 kJ/mol).
RRHO; ZPE scaled by
Hessian analysis.
IRC calculations.
*Estimated uncertainty – 24 kJ/mol

8. Quantum Chemistry Results

9. Synthesis of N-benzoylsulfonamides
18O-Benzoyl chloride contained 70% 18O
Solvent – pyridine
Media – triethylamine (substrate : TEA = 1 : 500)
Time – 20 min
Temperature – 25oC

10. Mass Spectra of N-Benzoyl-p-toluenesulfonamide
and it’s 18O Analog

11. Mass Spectra of 4-Acetylamino-N-benzoylbenzenesulfonamide,
Methyl- 4-(aminosulfonyl)phenylimidoformate and their 18O Analogs

12. Mass Spectra of N-Benzoyl-4-perfluoroacylamino-benzenesulfonamides

13. Mass Spectra of 3-Methyl-, 4-Chloro-, 4-Bromo-
and 4-Fluoro-N-methyl-N-phenylbenzamides

14. N-Methyl-N-phenylbenzamide
Base peak is m/z 105, PhCO+
m/z 118 is only 2.2% relative intensity
Computational results shown below
Entropy/DOS needed to explain base peak:
DG298 = 142 kJ/mol for m/z 105
DG298‡ = 164 kJ/mol for first high barrier
DG298‡ = 154 kJ/mol for 2nd high barrier

15. CONCLUSSIONS
A skeletal rearrangement involving an amidic oxygen atom migration under EI conditions is detected and explained.
2. A mechanism via carboximidate transition state is established.