Potential functions of internal rotations in n-mononitroalkanes

Internal rotation is studied in n-mononitroalkanes, CH₃(CH₂) _n NO₂, n ?? 7, with the use of the B3LYP/6-311++G(3df, 3pd) and MP2/6-311++G(3df, 3pd) models. Conformations are investigated, and 36 potential functions (V(??)) for all rotations are found. It is shown that as the hydrocarbon chain becomes longer, the potential functions that describe particular molecular fragments change only negligibly beginning from a certain n. Such dependences of V(??) are presented in the form of generalized functions with averaged coefficients (V(??)_av). The V(??)_av values can be recommended for use in simulations. In molecules with n ?? 2, the phenomenon of ??top interactions?? (??movement interactions??) and the gauche effect (the equality between the total energies of gauche ⁺, gauche ^?, and trans-conformers) are observed.