Fourier transform IR spectra of the first generation dendrons built from thiophosphoryl core with terminal PCl groups, vinyl (G 1 ) and azide (G 2 ) functional group at the level of the core have been recorded. The optimized geometries of low energy isomers of G 1 and G 2 have been calculated by density functional (DFT) method at the PBE/TZ2P level of theory. DFT is used for analyzing the properties of each structural part (core, branches, surface). It was found that the repeated branching units of G 1 and G 2 contain planar OC 6 H 4 CHNN(CH 3 )P fragments. DFT results for the structure of G 1 and G 2 are in good agreement with X-ray diffraction measurements. A complete vibrational assignment is proposed for different parts of G 1 and G 2 . The global and local reactivity descriptors have been used to characterize the reactivity pattern of the core functional and terminal groups. Natural bond orbital (NBO) analysis has been applied to comparative study of charge delocalization. Our study reveals why azide group linked to phosphorus has a different reactivity when compared to organic azides.