THE VIBRATIONAL AND NMR-SPECTRA, CONFORMATIONS AND AB-INITIO CALCULATIONS OF AMINOMETHYLENE, PROPANEDINITRILE AND ITS N-METHYL DERIVATIVES

The IR and Raman spectra of aminomethylene propanedinitrile (AM) [H2N- CH=C(CN)(2)], (methylamino)methylene propanedinitrile (MAM) [CH3NH-CH= C(CN)(2)] and (dimethylamino)methylene propanedinitrile (DMAM) [(CH3)( 2)N-CH=C(CN)(2)] as solids and solutes in various solvents have been r ecorded in the region 4000-50 cm(-1). AM and DMAM can exist only as on e conformer. From the vibrational and NMR spectra of MAM in solutions, the existence of two conformers with the methyl group oriented anti a nd syn toward the double C=C bond were confirmed. The enthalpy differe nce Delta H-o between the conformers was measured to be 3.7 +/- 1.4 kJ mol(-1) from the IR spectra in acetonitrile solution and 3.4 +/- 1.1 kJ mol(-1) from the NMR spectra in DMSO solution. Semiempirical (AM1, PM3, MNDO, MINDO3) and ab initio SCF calculations using a DZP basis se t were carried out for all three compounds. The calculations support t he existence of two conformers anti and syn for MAM, with anti being 7 .8 kJ mol(-1) more stable than syn from ab initio and 8.6, 13.4, 11.6, and 10.8 kJ mol(-1) from AM1, PM3, MNDO, and MINDO3 calculations, res pectively. Finally, complete assignments of the vibrational spectra fo r all three compounds were made with the aid of normal coordinate calc ulations employing scaled ab initio force constants. The same scale fa ctors were optimized on the experimental frequencies of all three comp ounds, and a very good agreement between calculated and experimental f requencies was achieved.