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The density functional B3LYP method with the 6-31++G(d,p) basis set was used to investigate several N-nitroso- N′, N′-dimethylphenylurea biological molecules in MeCN solution. Geometries obtained from DFT calculation were used to perform natural bond orbital (NBO) analysis. The p characters of two nitrogen natural hybrid orbital (NHO), $\sigma_{\mathrm{N}_{3}\mbox{\scriptsize{--}}\mathrm{N}_{2}}$ bond orbitals, increase with increasing σ values of the substituents on the benzene, which results in a lengthening of the N-N bond. The p character of the oxygen NHO $\sigma_{\mathrm{O}_{1}\mbox{\scriptsize{--}}\mathrm{N}_{2}}$ bond orbital decreases with increasing σ values of the substituents on the benzene, which results in a shortening of the N=O bond. It is also noted that decreased occupancy of the localized $\sigma_{\mathrm{N}_{3}\mbox{\scriptsize{--}}\mathrm{N}_{2}}$ orbital occurs in the idealized Lewis structure, or increased occupancy of $\sigma_{\mathrm{N}_{3}\mbox{\scriptsize{--}}\mathrm{N}_{2}}^{*}$ of the non-Lewis orbital, and their subsequent impact on molecular stability and geometry (bond lengths) are also related to the resulting p character of the corresponding nitrogen NHO of the $\sigma_{\mathrm{N}_{3}\mbox{\scriptsize{--}}\mathrm{N}_{2}}$ bond orbital. In addition, the partial charge distribution on the skeletal atoms shows that the electrostatic repulsion or attraction between atoms can give a significant contribution to the intra- and intermolecular interaction. [ABSTRACT FROM AUTHOR]