The reaction pathways for the interaction of the nitrite ion with ethyl chloride and ethyl bromide in DMSO, solution were investigated at the ab initio level of theory, and the solvent effect was included through the polarizable continuum model. The performance of BLYP, GLYP, XLYP, OLYP, PBE0, B3PW91, B3LYP, and X3LYP density functionals has been tested. For the ethyl bromide case, our best ab initio calculations at the CCSD(T)/aug-cc-pVTZ level predicts product ratio of 73% and 27% for nitroethane and ethyl nitrite, respectively, which can be compared with the experimental values of 67% and 33%. This translates to an error in the relative Delta G(double dagger) of only 0.17 kcal mol(-1). No functional is accurate (deviation < 0.5 kcal mol(-1)) for predicting relative Delta G(double dagger). The hybrid X3LYP functional presents the best performance with deviation 0.82 kcal mol(-1). The present problem should be included in the test set used for the evaluation of new functionals.