Substituent effects on the ring‐chain tautomerism of some 1,3‐oxazolidine derivatives

The 14 and 70 eV electron ionization mass spectra of five sets (R 1  = Me, Et, i ‐Pr, t ‐Bu and Ph) of seven 2‐aryl‐4‐R 1 ‐substituted (Ar = C 6 H 4 X; X =  p ‐NO 2 , m ‐Br, p ‐Cl, H, p ‐Me, p ‐OMe and p‐ NMe 2 ) (1–5) and of seven 2‐aryl‐5‐phenyl‐substituted 1,3‐oxazolidines (6; for Ar, see above) were recorded to study their ring‐chain equilibria in the gas phase. These equilibria were also studied by 1 H NMR spectroscopy in CDCl 3 for compounds 5 and 6. A few 2,4‐ and 2,5‐dimethyl‐2‐aryl derivatives (7, 8: Ar = C 6 H 4 X; X =  m ‐Br, H and p ‐OMe) were studied both in CDCl 3 and in the gas phase. The main characteristics of the ring‐chain equilibria expressed by the variable Σ RA % of the ring and of the chain form proved to be a strong dependence on the nature of the substituents on C‐2 and C‐4. The results in the gas phase are compared with those in CDCl 3 . Copyright © 2008 John Wiley & Sons, Ltd.