Substituent effects on the gas-phase ring-chain tautomerism of 3,4,5,6-tetrahydro-2H-1,3-oxazines

Márta Juhász, F. Fülöp, Kalevi Pihlaja

Research output: Contribution to journalArticle

5 Citations (Scopus)

Abstract

The electron ionization mass spectra of five series of seven 2-aryl,4-R-substituted (R = Me, Et, i-Pr, t-Bu or Ph) 3,4,5,6-tetrahydro-2H-1,3- oxazines were recorded at 14 and 70 eV in order to study the ring-chain tautomeric equilibria in the gas phase. Certain fragment ions were associated with the ring or with the open-chain forms of the compounds. As in chloroform solution, the electron-withdrawing effect of the aryl substituent (p-NO 2, m-Br, p-Cl, H, p-Me, p-OMe and p-NMe2) shifts the equilibrium towards the ring form. The correlation of ring-chain equilibria (log K = [ring]/[chain]) with the Hammett σ+ constants of the aryl substituents was in general good or satisfactory although in some cases the p-NMe2 did not fit these correlations.

Original languageEnglish
Pages (from-to)3701-3710
Number of pages10
JournalRapid Communications in Mass Spectrometry
Volume21
Issue number22
DOIs
Publication statusPublished - 2007

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Oxazines
Gases
Electrons
Chloroform
Ionization
Ions

ASJC Scopus subject areas

  • Analytical Chemistry
  • Spectroscopy

Cite this

Substituent effects on the gas-phase ring-chain tautomerism of 3,4,5,6-tetrahydro-2H-1,3-oxazines. / Juhász, Márta; Fülöp, F.; Pihlaja, Kalevi.

In: Rapid Communications in Mass Spectrometry, Vol. 21, No. 22, 2007, p. 3701-3710.

Research output: Contribution to journalArticle

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AB - The electron ionization mass spectra of five series of seven 2-aryl,4-R-substituted (R = Me, Et, i-Pr, t-Bu or Ph) 3,4,5,6-tetrahydro-2H-1,3- oxazines were recorded at 14 and 70 eV in order to study the ring-chain tautomeric equilibria in the gas phase. Certain fragment ions were associated with the ring or with the open-chain forms of the compounds. As in chloroform solution, the electron-withdrawing effect of the aryl substituent (p-NO 2, m-Br, p-Cl, H, p-Me, p-OMe and p-NMe2) shifts the equilibrium towards the ring form. The correlation of ring-chain equilibria (log K = [ring]/[chain]) with the Hammett σ+ constants of the aryl substituents was in general good or satisfactory although in some cases the p-NMe2 did not fit these correlations.

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