Comprehensive DFT and NMR studies on sparteine derivatives substituted in C2 position

The equilibrium structures of nine C2 sparteine derivatives have been investigated with the density functional theory, using the B3LYP method. The substituents at C2 position have been a methyl-, phenyl-, p-tolyl- or a cyano group. For all derivatives investigated the dominant conformer is that with the boat-chair system of the C/D rings. The NMR chemical shifts, calculated by the continuous set of gauge transformations formalism with the DFT/B3LYP method, have been correlated with experimental ones. The marked dependence of nuclear shielding and chemical shift on the torsional movement in 2-phenylsparteine and 2-(p-tolyl)sparteine have been observed. Moreover, the calculations performed for this compound show that the orientation of the phenyl ring in CDCl3 solution is different than that in solid state. In all compounds, the correlations between the calculated screening constants are better for carbon atoms than for protons.