THE VIBRATIONAL AND NMR-SPECTRA, CONFORMATIONS AND AB-INITIO CALCULATIONS OF METHOXYMETHYLENE-PROPANEDINITRILE AND 1-METHOXYETHYLIDENE-PROPANEDINITRILE

The IR and Raman spectra of methoxymethylene-propanedinitrile [H3C-O-C H-C(CN)(2)] and 1-methoxyethylidene-propanedinitrile [H3C-O-C(CH3)=C(C N)(2)] as a solid, liquid ant solute in various solvents have been rec orded in the region 4000-50 cm(-1). NMR spectra of both compounds in v arious solvents at different temperatures were also obtained. Semiempi rical (AM1, PM3, MNDO, MINDO3), ab initio using DZP basis sets and DFT calculations using B3LYP with 6-31G* basis sets were carried out for both compounds. These calculations support the idea on the existence of two conformers with a planar C=COC moiety and with the methyl group oriented as anti and syn towards the C=C double bond. The calculated small energy difference between them suggests the presence of born in the samples at room temperature. In contrast with the calculations, on ly one conformer has been found in the liquid vibrational and NMR spec tra. Complete assignments of the vibrational spectra for the compounds mentioned were made with the aid of normal coordinate calculations em ploying scaled ab initio and DFT force field constants. The scaled ab initio and DFT frequencies indicate that the conformer present in the liquid (solutions) and solid phases is anti. (C) 1997 Elsevier Science B.B.