MP2/6-311++G(d,p) calculations were performed on ethane and its simple derivatives. Different substituents such as: Li, Na, BeH, BH2, OH, NH2, F and NO2 were considered. The mono- and disubstituted derivatives of ethane were analyzed. The quantum theory of "atoms in molecules" was applied, to localize bond critical points and to analyze relationships between their locations and characteristics of the species. The numerous correlations were found showing the crucial influence of substituent effects. It was also revealed that such parameters as the carbon-carbon distance, or the electron density at C-C bond critical point do not show the systematic changes caused by substituent effects. This means that some of QTAIM parameters, especially the positions of BCPs may be useful to detect numerous sensitive effects if the latter ones do not affect the traditionally analyzed geometrical parameters of a molecule, such as bond lengths.