Theoretical study on stability and NMR chemical shifts of the diketene molecule, its isomers and their mono- and disulphur analogues

Theoretical Gibbs free energies have been determined for a set of cycloaddi tion products of allene. with CO2, CS2 or OCS molecules, and of CH2=C=X wit h CH2=C=Y molecule (X, Y = O, S). Each of the cycloaddition reactions leads to one or two isomeric products with four-membered heterocyclic ring. Theo retical thermochemical data suggest that the isomers in which sulphur atom is build into the four-membered ring can be easily formed in different reac tions whereas formation of those with oxygen atom in the ring strongly depe nds on the considered reaction. Analysis of the theoretical H-1 and C-13 ch emical shifts forms a basis for the detection of the isomer traces in react ion mixtures as well as for the elucidation of future experimental spectra. (C) 2001 Elsevier Science B.V. All rights reserved.