VIBRATIONAL-SPECTRA AND ROTATIONAL-ISOMERISM OF BIS(N-2-CHLOROETHYL)NITRAMINE

The IR and Raman spectra of bis(N-2-chloroethyl)nitramine (BCENA) in t he liquid and crystalline states and in CCl4 and CH3CN solutions are s tudied. The spectra are compared and if is concluded that BCENA exists as a mixture of conformers of different polarities in the liquid stat e and as one less polar conformer in the crystalline state. To determi ne the conformations corresponding to the total electron energy minima and interpret the vibrational spectrum of BCENA, we performed an ab i nitio quantum chemical calculation of the BCENA molecule in the Hartre e-Fock approximation using the 3-21G and 6-31G* basis sets. Out of tw elve possible conformations five are stable; the most stable conformer is C-2(GG). The frequencies and forms of normal vibrations of stable conformers are calculated using scaled quantum chemical force fields. The calculated and experimental frequencies are compared and the relat ions between the frequencies of skeletal stretching and bending vibrat ions are analyzed. It is concluded that the BCENA crystal is formed by the C-2(GG) conformer. The vibrational spectrum is interpreted, and t he frequencies are assigned to vibrations of conformers differing in f orm.