Ab initio B3LYP/6-31G(d,p) within the frame of Density Functional Theory was used to calculate the relative energies of the rotamers in the axial and equatorial chair conformations of 2-dimethylposphinoyl-1,3-dithiane and gauche-anti conformations of dimethylphosphinoyl(methylsulfanyl)methane The theoretical energy differences and geometric patterns are similar to those determined experimentally for the diphenylphosphinoyl analogue. The electrostatic nature of hydrogen bonds in the title molecules studied was analyzed through the Topological Theory of Atoms in Molecules (AIM). The bonding paths C-H ... X-P (X = O, S), as well as the properties of the: critical points associated with them at the B3LYP/6-31G(d,p)//(BP+NLSCF)/ DZVP2 level of theory, an described. The characterization of the H-X (X = O, S) bond path is relevant because it allows one to establish that interactions of the hydrogen-bond type can make a stabilizing contribution to the axial and gauche preferences of the segments studied hen. From the results of this paper, it is clear that the AIM method is suitable for the study of the interaction between a small polarity C-H donor and a good acceptor, such as the oxygen or sulfur atom bonded to phosphorus.