The vibrational and NMR spectra, conformations and ab initio calculations of phenylaminomethylene- and 1-phenylaminoethylidene-propanedinitrile

The IR and Raman spectra of (phenylamino)methylene-propanedinitrile [Ph-NH- CH=C(CN)2] (PAM) and (1-phenylamino)ethylidene-propanedinitrile [Ph-NH-C(CH 3)=C(CN)2] (PAE) as a solid and solute in various solvents were recorded in the region 4000-50 cm(-1). NMR spectra of both compounds in various solven ts at different temperatures were also obtained. Semiempirical (AM1, PM3, M NDO, MINDO3), ab initio using DZP basis set calculations were carried out f or the both compounds. These calculations support the idea on the existence of two conformers with a nearly planar C=CNHC moiety and with the phenyl g roup oriented as s-anti and s-syn towards the C=C double bond. The calculat ed high energy difference between them suggests the presence of only one co nformer in solutions at room temperature. In agreement with the calculation s, only one conformer was found in the vibrational and NMR spectra of the P AM solute. But some uncertain evidences for the second conformer were found in the vibrational spectra of the PAE solute, Complete assignments of the vibrational spectra for the compounds mentioned were made with the aid of n ormal coordinate calculations employing scaled ab initio force field consta nts. The scaled ab initio frequencies indicate that for both compounds the conformer present in the solutions and solid phase is s-anti. (C) 1999 Else vier Science B.V. All rights reserved.