Oxirane ring conformational effect

The coupling constants strongly suggest the half-chair conformation in the 2,3-and 3,4-anhydropyranosides, in which the conformational effect of the oxirane ring is similar to that of a double bond (2,3-unsaturated pyranoside derivatives). The C- H coupling constant can be determined from the C satellites of the proton spectrum and from the C spectrum. ... 

The conformation of cycloheptene oxide has been examined via the C nmr spectra of deuterated compounds on the basis of the temperature-dependence of the chemical shifts of the individual signals. In phenyl-substituted oxiranes, the C shifts have revealed the inductive and hyperconjugative effects of the oxirane ring, and thus the ring behaves as an electron-acceptor. " ... 

The n.m.r. spectra for (112 X = O, NH, S, or SO) have been recorded and compared with that for (112 X = CH2). The annelation effects of the three-membered rings were determined. Using 350 MHz n.m.r. and dipole moments, (113 R = H) and (113 R = OMe) were shown to adopt a boat conformation, with the 0 of the oxiran ring in a pseudo-axial position. The absolute configuration of alliacolide (116) has been established by c.d. 

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