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

Abstract

The IR and Raman spectra of (phenylamino)methylene-propanedinitrile [Ph–NH–CHC(CN)2] (PAM) and (1-phenylamino)ethylidene-propanedinitrile [Ph–NH–C(CH3)C(CN)2] (PAE) as a solid and solute in various solvents were recorded in the region 4000–50cm−1. NMR spectra of both compounds in various solvents at different temperatures were also obtained. Semiempirical (AM1, PM3, MNDO, MINDO3), ab initio using DZP basis set calculations were carried out for the both compounds. These calculations support the idea on the existence of two conformers with a nearly planar CCNHC moiety and with the phenyl group oriented as s-anti and s-syn towards the CC double bond. The calculated high energy difference between them suggests the presence of only one conformer in solutions at room temperature. In agreement with the calculations, only one conformer was found in the vibrational and NMR spectra of the PAM 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 normal coordinate calculations employing scaled ab initio force field constants. The scaled ab initio frequencies indicate that for both compounds the conformer present in the solutions and solid phase is s-anti.