The subject of our interest is the influence of molecular geometry on carbon-carbon spin-spin couplings. As models we have chosen enaminoketones of a general formula:

which can exist in the form of configurational E and Z (around a C=C bond) and conformational s-Z/s-E (relating to C-C(O) and C-N bonds) isomers. As a result, a single compound of type B can potentially encompass eight, mutually interconverting stereoisomeric forms providing a wealth of conformational structures. The equilibrium between them strongly depends on the bulkiness of alkyl substituents, polarity of solvent and temperature.

Computational methods are very helpful in this kind of structural investigations. Especially density functional theory (DFT), in particular with the Becke-3-parameter-Lee-Yang-Parr (B3LYP) hybrid functional, has been shown to be a promising method for the calculation of indirect nuclear spin-spin coupling constants.

In the present communication configurational and conformational studies of two enaminoketones: 4-methylamino-but-3-en-2-one (1) and 4-dimethylamino-but-3-en-2-one (2) have been performed with using of the DFT method and experimental measurements (the INADEQUATE technique) [1]. We attempt to answer the important practical question of how well theoretical values predict experimental spin-spin coupling constants in our model compounds.

Scheme: Possible conformations of enaminoketones studied. Full geometry optimization and spin-spin couplings calculations were carried out using the Gaussian03 facilities [2] at the DFT[B3LYP/6-311++G(2d,p)//B3LYP/6-311++G(2d,p)] level. Only the underlined species were observed in experimental measurements.

[1] M. Bugaj, K. Kamieńska-Trela, Pol. J. Chem. 2006 (accepted for publication).
[2] M. J. Frisch et. al., Gaussian03, Revision B.05, Gaussian Inc., Pittsburgh, PA, 2003.

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