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Substituent effects on the gas‐phase ring‐chain tautomerism of 3,4,5,6‐tetrahydro‐2 H ‐1,3‐oxazines
Author(s) -
Juhász Márta,
Fülöp Ferenc,
Pihlaja Kalevi
Publication year - 2007
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.3260
Subject(s) - chemistry , substituent , tautomer , ring (chemistry) , aryl , oxazines , medicinal chemistry , chain (unit) , stereochemistry , hammett equation , gas phase , alkyl , organic chemistry , reaction rate constant , kinetics , physics , quantum mechanics , astronomy
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‐2 H ‐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 ‐NMe 2 ) 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 ‐NMe 2 did not fit these correlations. Copyright © 2007 John Wiley & Sons, Ltd.