Structure-NMR chemical shift relationships for novel functionalized derivatives of quinoxalines

H-1, C-13 and N-15 NMR chemical shifts for a variety of novel quinoxalines were determined by different 2D methods and were calculated using the GIAO DFT approach. Comparison with experimental data shows good correlations in the case of H-1, C-13 and N-15 chemical shifts. Different combinations of basis sets were tested. In non-polar solvents quinoxalines exist as dimers owing to strong hydrogen bonding. Calculations for dimers improve the correlation between experiment and theory. Additive empirical methods for estimating chemical shifts have drawbacks and have to be used with a great care for this type of compound. Copyright (c) 2005 John Wiley & Sons, Ltd.