The BLYP and B3LYP density functional methods and a series of basis sets,6-31G,6-31G^*,6-31G^*^*,6-311G,6-311G^* and 6-311G^*^*,have been used to calculate the molecular geometries and infrared spectra of methyl and ethyl nitrates.It is shown that BLYP method is not suitable for calculating the geometry and IR frequencies of organic nitrates no matter what kind of basis set is used. While B3LYP calculations produce satisfactory results when polarization bases(6- 31G^*,6-31G^*^*,6-311G^*and6-311G^*^*) are used.The standard themodynamic functions calculated using the B3LYP/6-31G^* frequencies scaled by 0.975 are in good agreement with the available experimental results.

Key words: METHYL NITRATE, ETHYL NITRATE, THERMODYNAMIC PROPERTIES, GEOMETRICAL ISOMERISM, FREQUENCY OF VIBRATION