Nuclear magnetic resonance spectra of some inorganic ring systems. Part 1.—Proton resonance spectra of 1,3-diaza-2-thiacyclopentanes

Abstract

The proton magnetic resonance spectra of the ring systems (I) and (II) below show that there is a non-equivalence of the protons in both the ring-methylene and ethyl-methylene groups for all compounds, with the exception of the ring-methylene protons in (II). The non-equivalence in each case is attributed to the presence of the sulphoxide or sulphone group. The asymmetry at the sulphur atom, causing the absence of a plane of symmetry in the five-membered ring, is the primary cause of ring-methylene non-equivalence. The absence of a plane of symmetry containing the N—R bond makes the side-chain methylene protons non-equivalent, but an additional factor may be the restricted rotation about the C—N bond. The spectra are analyzed to evaluate chemical shifts and coupling constants, and a theoretical spectrum is computed for the methylene signals of (I)(R = Et).