AbstractThe n.m.r. spectra of various derivatives of the cyclic acylal of malonic acid and of dimethylbarbituric acid are described. From the long range coupling constant, conformational evidence on the dihedral angle θ between the aromatic ring and the diketodioxane ring or theN,N‐dimethylbarbituric acid ring can be derived. The investigated substances show a dependence of θ on the aromatic substitut