CH, CD, CC and HH coupling constants in isotopically enriched cyclobutene

Abstract 1 H, 2 H and 13 C NMR studies of cyclobutene and a series of isotopically enriched species have led to a determination of the 1 H 1 H, 13 C 1 H, 13 C 2 H and 13 C 13 C coupling constants in these compounds. In agreement with general observations, 1 J (CH) is found to depend on the hybridization of the carbon atoms. Likewise, 2 J (HH), 2 J (CC), 3 J (HH) and 3 J (CH), but not 2 J (CH), depend on the angles between the bonds connecting the coupled nuclei. When comparing cyclobutene with thiete 1,1‐dioxide (thiete sulphone) an increase of almost 20 Hz is observed for 1 J (C‐2, H‐2) in the latter compound. All but one of the observed deuterium isotope effects on chemical shifts are negative. In the case of isotope effects upon the one‐bond coupling constants, the obtained values support the results of the theoretical calculations of Sergeev and Solkan.